This is definitely good to know, especially if you don't us a rebate site. I buy a lot of stuff on ebay and I have an AMEX Premier Rewards card which gives you 2 points per dollar at grocery stores, so I buy ebay gift cards at the grocery store and use one of the rebate sites to get some cash back (around 3-4%), plus another 1-2% back for the ebay bucks program. Works out to be a decent deal for a lot of items. I just make sure not to use a gift card if I'm buying something where I think there is a chance where I may need the dispute charge option of a credit/charge card.