Plato, Laws 917d

νῦν πείθεσθαι λόγοις, ὁ προστυγχάνων τῶν γιγνωσκόντων, δυνατὸς ὢν ἐξελέγχειν, ἐναντίον ἐλέγξας τῶν ἀρχόντων, ὁ μὲν δοῦλος φερέσθω τὸ κιβδηλευθὲν καὶ ὁ μέτοικος, ὁ δὲ πολίτης μὴ ἐλέγχων μὲν ὡς ἀποστερῶν τοὺς θεοὺς κακὸς ἀγορευέσθω, ἐλέγξας δὲ ἀναθέτω τοῖς τὴν ἀγορὰν ἔχουσιν θεοῖς. ὁ δὲ δὴ φανερὸς γενόμενός τι πωλῶν τοιοῦτον, πρὸς τῷ στερηθῆναι τοῦ κιβδηλευθέντος, ὁπόσης ἂν τιμῆς ἀξιώσῃ τὸ πωλούμενον, κατὰ δραχμὴν ἑκάστην τῇ μάστιγι

and is incapable of obeying our present rules, any person who is present and aware of the fact and able to expose him shall take for himself the adulterated article, if he expose him before a magistrate, he being himself a slave or a metic,—but if he be a citizen, he shall be declared to be wicked, as a robber of the gods, if he fail to expose the guilty man; while if he does expose him, he shall offer the article to the gods who preside over the market. He that is found out in selling any such article, in addition to being deprived of the adulterated article, shall be beaten in the market-place with stripes—one stripe for every drachma in the price he asks for the article—