I bought two World of Warcraft accounts on Playerauctions.com, and was extremely worried about the security of a purchased account as the original owners can take them back relatively easily. However, playerauctions boasts about their "playerguardian" protection, in which you will get a complete refund in the form of a store credit in the event that an account is stolen back by the seller or becomes unrecoverable for a reason out of the buyers hands.
Both accounts that I bought were taken back by the original owners. Both characters were transferred back to their original servers with their original names, and only the original owners could have had the authenticator linked to each account disabled (you have to call Blizzard directly). I sent playerauctions screenshots, email records about the account information being changed etc... everything that I could possibly have short of an email saying "hello, I am the person who sold you the account and I have stolen it back".
I got the same reply from playerauctions about both accounts saying that there was not enough proof that the seller had taken the account back. They want evidence that simply does not exist, making it impossible for you to prove anything and get a refund. I have been a member of playerauctions since 2003 and have a 100% positive feedback rating for over 35 auctions (my name is Tarewmonk if you would like to check), and they couldn't care less about my satisfaction.
I don't expect to get a refund as I have already tried numerous times over the past couple of months, so I'm posting this as a warning to anybody who is looking to buy an account from playerauctions - there is absolutely nothing you can do if an account you buy is stolen back.