Yes, you could but the buyer beware if you purchase from other than authorized official manufacturers dealers. Some manufacturers will not honor their warranty if you buy on ebay or other auction sites (see example below) Also, these individuals, more often then not, are no where to be found if you have a problem or question later.
Examples:
Superchips Policy
DiabloSport read section 5.b.iii b "Product must be purchased at an DiabloSport Authorized Dealer in order to qualify for warranty"
I'm not saying that you shouldn't buy anything on these auction sites, just that make sure you understand what you are doing. We get quite a few customers calling us asking us for warranty/tech support on products that we carry, but that they bought on auction sites. They contacted the manufacturer for support, but were told to get support through the store they bought the item from. They call us to see if there is anything we can do. we'd like to help, but we don't take returns of this nature as you can imagine. Just be careful, is all I'm saying.