last week at the bakery I asked for one half dozen rolls among other items with my order. On Shabbos, we noticed that the lady accidently gave me seven rolls. I only needed six, and that is all I paid for. Am I required to pay now for the seventh roll? Should I have put it away and offer to return it on Sun morning, requiring a special trip to give back a roll which would then be two days old? Could I just eat it on Shabbos? We ended up eating it, do I have to pay now?
The roll that was eaten must be paid for, becasue it has a known price, and was eaten knowingly. Had it not been eaten, you would have reserved the right to return it to the shop. It would be sufficient to notify the shop, and it would be their responsibility to pick it up, or, it it would not be worthwhile for them, to give it away. Of course, you can call up the bakery and ask the owner if he demands payment (which he is in his right to do), or if he is prepared to forgo it.
Sources: The Gemara in Bava Kama (112a) discusses a case in which orphans ate somebody else’s cow, thinking it was theirs. The Gemara writes that they must pay the owner, but they pay a reduced sum. In our case, however, it was known that the roll belonged to the bakery and was delivered by mistake, and the full price must be paid, as we find in Kesubos 34a (concerning somebody who was force-fed) and in Tosefos (Bava Kama 20b). However, before the roll was eaten it is permissible to put it away and return it after Shabbos, as with every item of lost property. It was permitted to eat the roll, because this is a better form of returning lost property than returning a stale roll after Shabbos.