buy used games on xbox 360 and download them then return it back to the store?

Okay so the new xbox 360 lets you download games onto the hard drive, so what if I bought some used games at gamestop and download them to the hard drive and then return the games back for my money… would gamestop know about it?

downloading games to your hd require the genuine disc to work. if u dont have the disc… it wont run