Qitzur Shulchan Arukh – 63:4
It is prohibited to “steal the knowledge” of people; meaning, to mislead them with words. Even if there is no loss of money involved. Even the knowledge of idolaters.
Therefore, it is prohibited to sell him [an idolater] meat from an animal that died naturally under the presumption that it was slaughtered [according to halakhah]. If he sells any thing which has a defect, even if the item is worth the same as what he was selling it for, still he has to tell him about the defect. (See later, 182:4)
For a gift, there is no prohibition of misleading.
We discussed this earlier, on 62:7, where I also provided the halakhah at 182:4, which Rabbi Ganzfried refers us to. From 182:4:
What is fraud? One person obtains his peer’s money with his peer’s consent, such as he has a loan or rental payment, but he doesn’t want to repay him…
Since it says “rei’ekha — your neighbor”, it is not prohibited when [the victim is] a non-Jew and there is no risk of chilul hasheim (desecrating G-d’s reputation)…
Even in a situtaiton where [the non-Jew] does not know [and thus there is no risk of chilul Hashem], it is not permitted except to avoid a loan or some other debt that he owes him. However, an object which is visible, one may not use trickery, for this is actual theft. Not only that, but even if he bought an object from him, he can’t trick him in the calculations when paying him the money, as it says “and he shall reckon with him who bought him” [the verse in question is originally about a slave]. Which applies to a non-Jew, because he only gave over the ownership of the object for a payment which is equal. Therefore, someone who tricks him in the calculation of the money, it is like he stole the object, and not like he avoided his debt.
Even geneivas da’as (stealing knowledge; i.e. lying or intentionally giving a false impression) that does not cause a loss of money, is prohibited in commerce as I wrote in chapter 63. In any case, if the non-Jew errs himself, it is permissible — if there is no chilul hasheim — not to inform him. Although it is appropriate for the Jew to tell him, “I am relying on your calculations.”
Notice the term for fraud and lying, “geneivas daas“, theft of knowledge. Halakhah is rarely structured in terms of rights, but here that seems to be the clear intent. That people have a right to knowledge, and thus intentionally misleading someone is a form of theft.
Even more interesting, it would seem from 182:4 that the right to knowledge is more enforced, at least in the case of idolaters than property is! After all, one may make money on an honest mistake made by an idolatrous non-Jew in a case where the mistake would never be caught and lead to chilul Hashem. But if the non-Jew assumes something that makes no difference to him — e.g. whether an animal he bought would be kosher for Jews — we have to clear up an error in that assumption. Implicitely causing a misunderstanding, such as being a Jew who generally sells kosher meat, is also geneivas da’as. As I noted earlier, this seriously minimizes the scope in which money can be gained through misunderstanding as well.