I don't think they will ask anything... from what I remember from when I used mine is they just took them and scanned them like a normal receipt.
It won't hurt to try using it though. Worse that can happen is that they tell you that the original owner has to be present. Then you could just go to the store with the friend who gave it to you. Or, if its a friend that isn't close, have that friend contact the store to give you permission to use it maybe.
I don't think you should have any problems though, honestly. You could also just use the certificate online.