I recently sold my FAR ipod on ebay and I included a copy of the invoice receipt. I'm wondering if the person I sold it to can go into an Apple store with the receipt and exchange it for something else, thus resulting in Apple charging the amount of the rebate check back to my credit card?

My friend said that the serial number for the ipod is linked to the rebate in Apple's computer system so it won't let them get an exchange. Is this true? I know it's not likely, but it would suck if the person I sold it to decided to exchange it for something else and Apple charged me the amount of the rebate check.