I have long used:
http://www.ResellerRatings.com
when considering a new vendor for internet purchases. The ratings there are actually pretty solid. My hobby is photography and this place is the first cource used to make sure a deal is legit...a surprising number of fraudlent sites have been sleuthed out this way. And even the legit sites have info which can show their sales practices as well as how they handle problems.
It might even be nice if people here on POTN began rating ebook device sellers on the site.