Say I buy a food item at a supermarket and later discover it was opened. I then am unsure whether I opened it or not. Is one allowed to return it if there is doubt (one is not completely sure) that one may have forgotten and opened it?
A second example is say I buy an item that I believe to be kosher. I then realize it is not kosher after opening it but just before eating it. Is one allowed to return this item as well or should it just be thrown out because it was the fault of the consumer for not being more careful?