It's not illegal, but you probably should not do it. You will owe sale/use tax to the state of Wyoming for anything you buy online, even if you turn around and sell it to someone else. Some states may also require that you collect and remit sales tax to them for items you sell to their residents. If Amazon specifically limits use of its site to personal use, Amazon could pursue you for damages if you violated this. You would be competing with them, and they would have a real incentive to make an example of you.
Answered on Nov 26th, 2012 at 4:22 PM