There is an online form that you fill out stating what type of card you will be sending back. I don't really think that they would reject anything however. It's kind of like when car dealers do the push, pull or drag any car in for a minimum $3000 trade-in. What would they be doing with the old cards anyway? Maybe they have some poor sap in charge of reselling them on e-Bay or something, LOL.
Do keep in mind that you would be paying for the shipping of your old card to them, as well as probably paying shipping costs of the new card. This quickly brings the price up to near Newegg territory IMO.