Several Talmudic stories describe sages who took advantage of a non-Jew's arithmetical error — and they are preserved without varnish, because the rabbis wanted the argument to be lived, not hidden. Rabbi Shemuel once bought what a stranger thought was a copper plate for four zuzim, and then short-changed him by one. Rav Kahana bought a hundred and twenty casks of wine for a hundred zuzim and withheld one coin from the payment. Rava took the largest logs from a shared tree. Rav Ashi, walking past a vineyard, instructed his servant to bring grapes only if they belonged to a stranger.
The owner of the vineyard happened to be in earshot. "Is it lawful," he called out, "to rob a stranger?" The story breaks off mid-line — but later authorities did not leave the matter dangling. The halakhah, as ultimately fixed, forbids robbing or defrauding anyone, Jew or gentile, precisely because of chillul Hashem, the desecration of God's Name when a Jew behaves dishonestly with those outside the covenant.
The Talmud (Bava Kamma 113b) preserves these stories not to endorse sharp practice but to raise the argument and let the sharper voice win. Even when an earlier sage bent the rules, a later one straightens them. The honor of Heaven does not tolerate a bargain that cheats the stranger at the gate.