Q: I want to give an app as a gift, but I am not sure if the person already has it. What happens if the recipient already has the app you give them? Do they get a credit? Do I get a refund? Am I just out of luck?
A: Sending an iTunes Gift of any kind actually generates a redemption code; the gift itself is not actually downloaded until the recipient chooses to redeem the code by clicking on the link provided in the e-mail or entering it manually into the “Redeem” section on the iTunes Store. Gift codes are not specific to any user account or e-mail address and can actually be used by anybody who has the code.
So basically this ends up working much the same way as it would with a physical gift; the recipient of a gift code for an item that they already have would simply not redeem the code, choosing instead to either give it back to you or pass it on to somebody else. It’s worth noting, however, that Apple will not necessarily provide a refund for an unused gift code.
Note that if the recipient does in fact redeem the gift code for an app they already own, the app will be downloaded again and the code will be used. It’s probably a good idea to note somewhere in the e-mail message that they should only use the code if they don’t already have the app in question.