Asking me to enter my Amazon username and password makes this a complete non-starter. Might be the best idea in the world, but I'm not going to risk handing over my credentials for something as sensitive as my Amazon account to make a few extra bucks on some old stuff. There's just not enough risk-reward there for me (though with all due respect and in all honesty, it's unlikely there would ever be enough reason for me to hand over my credentials to some random startup)