After talking with VietGamer and asking for some evidence (which he was happy to provide very quickly) we completed the transaction (with me going first).
Everything went very smoothly, and I am now enjoying the d3 beta! Secret question and all relevant details were provided instantly upon payment.
Many people seeking to sell and buy d3 accounts (me included) find this site only via a google search, and thus do not have many posts to vouch for them. While I cannot say everyone is legitimate (as there have been scammers) I am very happy to say that VietGamer was legitimate and completely honest.
As I have very few posts take it with a grain of salt... but I advise everyone looking to buy an account just to make sure that the seller is honest with some evidence, or that they are willing to use a middleman etc.
Just my 2 cents!