This verse is by its meaning so closely connected with Ecclesiastes 9:18 that the selection of it for the beginning of a new chapter seems unfortunate.
Apothecary - Rather: a dealer in spices and perfumes (compare Exodus 30:25). The swarms of flies in the East very soon corrupt and destroy any moist unguent or mixture left uncovered, and pollute a dish of food in a few minutes.
So doth - literally, more weighty than wisdom, than honor, is a little folly.

Dead flies - Any putrefaction spoils perfume; and so a foolish act ruins the character of him who has the reputation of being wise and good. Alas! alas! in an unguarded moment how many have tarnished the reputation which they were many years in acquiring! Hence, no man can be said to be safe, till he is taken to the paradise of God.

Dead flies cause the ointment of the apothecary to send forth a stinking savour,.... Such, as Jarchi observes, are in the winter season, which are weak and near to death, and get into precious ointment, prepared after the best manner, where they die, and corrupt and spoil it: or, "flies of deaths" (m); deadly ones, which have something in their nature poisonous and pernicious; which, when they light upon the most sweet and savoury ointment, give it an ill smell;
so doth a little folly him that is in reputation for wisdom and honour; a good name is like precious ointment, valuable and fragrant; sin, which is folly, is like a dead fly; not only light and mean, and base and worthless, but hurtful and pernicious, deadly, and the cause of death; and what may seem little, a peccadillo, or, however, one single act of sin, may injure the character of a wise and honourable man, and greatly expose him to shame and contempt, and cause him to stink in the nostrils of men, Genesis 36:20; and to be reproached by men, and religion and government to be reproached for his sake. Thus the affair of Bathsheba and Uriah, what a slur did it bring on the character of David, so famous for wisdom and honour, for religion and piety? and the idolatry of Solomon, the wisest of men; Jehoshaphat, that good king, entering into affinity with Ahab; and pious Josiah going to war with the king of Egypt, contrary to the word of the Lord; with many other instances. This teaches how careful men eminent for gifts and grace should be of their words and actions; since the least thing amiss in them is easily discerned, and soon taken notice of, as the least speck in a diamond, or spot in fine linen, clean and white; and there are wicked and envious persons enough watching for their halting, glad to have an occasion against them, and improve everything to the uttermost: this is a caution to wise magistrates, honourable ministers of the word, and eminent professors more especially. The Targum is,
"evil concupiscence, which dwells at the gates of the heart, is as a fly, and is the cause of death in the world; and corrupts a good name, which was before like to anointing oil, perfumed with spices:''
and to the same purpose the Midrash. One of the names of Satan is Beelzebub, the lord of a fly; who, by his temptations, solicits to sin and folly, which produce the effect here mentioned, and therefore to be shunned as a deadly fly in the ointment, Matthew 12:24. Gussetius (n) renders it,
"that which is precious and worthy of honour "proceeds" from wisdom; and folly "comes" from glory, "worldly glory", in a little time.''
(m) "muscae mortis", Montanus, Vatablus, Drusius, Amama, Cocceius, Rambachius. (n) Ebr. Comment. p. 344.

Those especially who make a profession of religion, should keep from all appearances of evil. A wise man has great advantage over a fool, who is always at a loss when he has anything to do. Sin is the reproach of sinners, wherever they go, and shows their folly.

(Ecclesiastes. 10:1-20)
Following up Ecclesiastes 9:18.
him that is in reputation--for example, David (2-Samuel 12:14); Solomon (1Ki. 11:1-43); Jehoshaphat (2Ch. 18:1-34; 2-Chronicles 19:2); Josiah (2-Chronicles 35:22). The more delicate the perfume, the more easily spoiled is the ointment. Common oil is not so liable to injury. So the higher a man's religious character is, the more hurt is caused by a sinful folly in him. Bad savor is endurable in oil, but not in what professes to be, and is compounded by the perfumer ("apothecary") for, fragrance. "Flies" answer to "a little folly" (sin), appropriately, being small (1-Corinthians 5:6); also, "Beelzebub" means prince of flies. "Ointment" answers to "reputation" (Ecclesiastes 7:1; Genesis 34:30). The verbs are singular, the noun plural, implying that each of the flies causes the stinking savor.

The second half of the foregoing double proverb introduces what now follows: "Poisonous flies make to stink, make to ferment the oil of the preparer of ointment; heavier than wisdom, than honour, weighs a little folly." We do not need to change מות זבוּבי, on account of the foll. sing. of the pred., either into זבוגי ם (as possible by Hitz.) or זב ימוּתי (Luzz.); both are inadmissible, for the style of Koheleth is not adorned with archaisms such as Chirek compaginis; and also such an attrib. clause as זבוב ימות, a fly which dies," is for him too refined; but both are also unnecessary, for a plur. of the subj., in which the plurality of the individuals comes less into view than the oneness of their character, is frequently enough followed by the sing. of the pred., e.g., Genesis 39:22; Joel 1:20; Isaiah 59:12, etc. It is a question, however, whether by זבובי מות, death-bringing, i.e., poisonous flies (lxx, Targ., Luther)
(Note: The Targ. interprets, as the Talm. and Mid. do, deadly flies as a figure of the prava concupiscentia. Similarly Wangemann: a mind buried in the world.)
or dead flies (Symm., Syr., Jerome) is meant. We decide in favour of the former; for (1) זבובי מות for זבוּבים מתים (Ecclesiastes 9:4; Isaiah 37:36), "death-flies" for "dead flies," would be an affected poetic expression without analogy; while, on the contrary, "death-flies" for "deadly flies" is a genit. connection, such as מות כּלי instruments of death, i.e., deadly instruments and the like; Bttcher understands dung-flies; but the expression can scarcely extend to the designation of flies which are found on dead bodies. Meanwhile, it is very possible that by the expression זב ם, such flies are thought of as carry death from dead bodies to those that are living; the Assyr. syllabare show how closely the Semites distinguished manifold kinds of זבובים (Assyr. zumbi = zubbi). (2) In favour of "dead flies," it has been remarked that that influence on the contents of a pot of ointment is effected not merely by poison-flies, but, generally, by flies that have fallen into it.
But since the oil mixed with perfumes may also be of the kind which, instead of being changed by a dead body, much rather embalms it; so it does not surprise us that the exciter of fermentation is thus drastically described by μυῖαι θανατοῦσαι (lxx); it happens, besides, also on this account, because "a little folly" corresponds as a contrasted figure to the little destructive carcase, - wisdom בע תּח ("giveth life," Ecclesiastes 7:2), a little folly is thus like little deadly flies. The sequence of ideas יב יבּ (maketh the ointment stink) is natural. The corrupting body communicates its foul savour to the ointment, makes it boil up, i.e., puts it into a state of fermentation, in consequence of which it foams and raises up small blisters, אבעבועות (Rashi). To the asyndeton יב יבּ, there corresponds, in 1b, the asyndeton מח מ כּ; the Targ., Syr., and Jerome,
(Note: The lxx entirely remodels Ecclesiastes 10:1: τίμιον κ.τ.λ ("a little wisdom is more honour than the great glory of folly"), i.e., יקר מעט חכמה סכלות רב (כבוד in the sense of "great multitude"). Van der Palm (1784) regards this as the original form of the text.)
who translate by "and," are therefore not witnesses for the phrase וּמך, but the Venet. (καὶ τῆς δόχης) had this certainly before it; it is, in relation to the other, inferior in point of evidence.
(Note: מכּבוד; thus in the Biblia rabb. 1525, 1615, Genoa 1618, Plantin 1582, Jablonski 1699, and also v. d. Hooght and Norzi. In the Ven. 1515, 1521, 1615, וּמכּבוד is found with the copulat. vav, a form which is adopted by Michaelis. Thus also the Concord. cites, and thus, originally, it stood in J., but has been corrected to מכּבוד. F., however, has מכּבוד, with the marginal remark: מכבוד כן קבלתי מני שמשון (Simson ha-Nakdam, to whom the writer of the Frankf. Cod. 1294 here refers for the reading מך, without the copul. vav, is often called by him his voucher). This is also the correct Masoretic reading; for if וּמך were to be read, then the word would be in the catalogue of words of which three begin with their initial letter, and a fourth has introduced a vav before it (Mas. fin. f. 26, Ochla veochla, Nr. 15).)
In general, it is evident that the point of comparison is the hurtfulness, widely extending itself, of a matter which in appearance is insignificant. Therefore the meaning of Ecclesiastes 10:1 cannot be that a little folly is more weighty than wisdom, than honour, viz., in the eyes of the blinded crowd (Zckl., Dchsel). This limitation the author ought to have expressed, for without it the sentence is an untruth. Jerome, following the Targ. and Midrash, explains: Pretiosa est super sapientiam et gloriam stultitia parva, understanding by wisdom and honour the self-elation therewith connected; besides, this thought, which Luther limits by the introduction of zuweilen ["folly is sometimes better than wisdom, etc."], is in harmony neither with that which goes before nor with that which follows.
Luzz., as already Aben Ezra, Grotius, Geiger, Hengst., and the more recent English expositors, transfer the verbs of Ecclesiastes 10:1 zeugmatically to Ecclesiastes 10:1: similiter pretiosum nomine sapientiae et gloriae virum foetidum facit stolidtias parva. But יביע forbids this transference, and, besides, מן יקר, "honoured on account of," is an improbable expression; also מך יקר presents a tautology, which Luzz. seeks to remove by glossing מך, as the Targ. does, by ונכסים עושר מרוב. Already Rashi has rightly explained by taking יקר (Syr. jaḳîr, Arab. waḳur, waḳûr), in its primary meaning, as synon. of כּבד: more weighty, i.e., heavier and weighing more than wisdom, than honour, is a little folly; and he reminds us that a single foolish act can at once change into their contrary the wisdom and the honour of a man, destroying both, making it as if they had never been, cf. 1-Corinthians 5:6. The sentence is true both in an intellectual and in a moral reference. Wisdom and honour are swept away by a little quantum of folly; it places both in the shade, it outweighs them in the scale; it stamps the man, notwithstanding the wisdom and dignity which otherwise belong to him, as a fool. The expressive רקח שׁמן is purposely used here; the dealer in ointments (pigmentarius) can now do nothing with the corrupted perfume, - thus the wisdom which a man possesses, the honour which he has hitherto enjoyed, avail him no longer; the proportionally small portion of folly which has become an ingredient in his personality gives him the character of a fool, and operates to his dishonour. Knobel construes rightly; but his explanation (also of Heiligst., Elst., Ginsb.): "a little folly frequently shows itself more efficacious and fruitful than the wisdom of an honoured wise man," helps itself with a "frequently" inserted, and weakens מך to a subordinated idea, and is opposed to the figure, which requires a personality.