Many in-store rebate offers are paid off in merchandise, often in the form of gift-cards. That's an easy way of inflating the face value of the rebate. When a store or manufacturer gives you a cash rebate, they're out exactly the amount of money you receive. But when they give you a gift-card, they are actually only out their cost of whatever you redeem the card for. Depending on the store's markup percentage, that may be as little as 50% of the face value of the card.

And, of course, giving you a rebate that can only be redeemed at their store is a sure-fire way to get you back through the door where, they hope, you'll probably spend way more than the face value of the gift-card they sent you.