You only receive the serial key, but that saves a lot of money.
Purchased over $700 worth of games, never had problems. Customer service is fast aswell ( didn't had a problem, just a question about a optional map-pack ) got a reply in like 5 minutes.
Ive inly used offgamers since it was mentioned on this forum, ive never had a problem with them, keys etc delivered in minutes inc scans for verification if Blizz ever requests it.