If someone purchased an item for me and I want to refund it, is that possible even though I don't have their credit card info or their signature or whatever? thanks

either that, or store credit. if it's a gift, then just tell the person and they'll take it back.

Totally depends on where the item was purchased. Some stores require the original credit card. If you don't have it for some reason, they will probably give you store credit. Some stores are really lenient and will give you cash.