I ordered something expensive from an online store. I found the item hefker in the lobby of the building I reside in. Am I allowed to tell the retailer that I did not receive the item? They just left it lying around publicly…
Although the person who delivered the item did a lousy job and didn’t put it in a safe place, nevertheless you took the item and you did receive it, and we are not allowed to lie even to a gentile. In addition, as you stated it would also be gnievas daas, as gneivas daas does apply to a gentile.