If you get too much change or some one does a business transaction wrong should you tell them? If you do keep the extra money form the transaction is this considered stealing if it was the other person’s fault?
With a Jewish counterpart you would be obligated to point out the error and keeping the money would be stealing, even if it was the other side’s error. Foe a non Jew you are not obligated to point out the mistake. However, if it will bring about a kiddush Hashem this would be a commendable practice.
See Rambam, Laws of Theft and Lost Property 11:3; the question of lehat’oso in alechatchilah sense is disputed among authorities, but most forbid it (rulings of Rambam 11:4, Mordechai, cited in Rema 348:2, Yam Shel Shlomo, Shulchan Aruch Harav, Onaah 11, and others).
The Gemara (Bava Kama 113) writes that the “mistake” of a non-Jew is permitted [many write that this applies specifically on a bedieved level, See Rambam, Hilchot Geneivah 7:8; Mordechai, end of Bava Basra (563); Chinuch 258; Yam Shel Shlomo Bava Kama 10:20; Machaneh Ephraim, Hilchot Gezeilah 4; see also Sema 283:6, 359:3].