Plato, Laws 920c

καθάπερ ἔμπροσθεν ἐπετάξαμεν τῆς κιβδηλείας πέρι, συγγενοῦς τούτῳ πράγματος, συνελθόντας δὲ ἰδεῖν λῆμμά τε καὶ ἀνάλωμα τί ποτε τῷ καπήλῳ κέρδος ποιεῖ τὸ μέτριον, γράψαντας δὲ θεῖναι τὸ γιγνόμενον ἀνάλωμα καὶ λῆμμα καὶ φυλάττειν, τὰ μὲν ἀγορανόμους, τὰ δὲ ἀστυνόμους, τὰ δὲ ἀγρονόμους· καὶ σχεδὸν οὕτως ἂν καπηλεία τὰ μὲν ὠφελοῖ ἑκάστους, σμικρότατα δὲ ἂν βλάπτοι τοὺς ἐν ταῖς πόλεσι χρωμένους.

in the case of the kindred matter of adulteration: the Law-wardens must meet in consultation with experts in every branch of retail trade, and at their meetings they must consider what standard of profits and expenses produces a moderate for the trader, and the standard of profits and expenses thus arrived at they must prescribe in writing; and this they must insist on—the market-stewards, the city-stewards, and the rural stewards, each in their own sphere. So possibly, by this means, retail trade would be of benefit to all classes, and would do but little damage to those in the States who practise it.