I recently got screwed trying to activate a receiver purchased from Ebay, and found something rather interesting. If you want to know if a receiver really, really really is clear to activate on another account, you have to all the audit team (888-371-9077). Standard CSR's may not read all the notes on an account, and tell you the receiver can be activated when it really cant. Be sure to get the name and operator ID of the person you talk to, and make note of the time and date you called in case you do get screwed later.
Also, if you do buy something on Ebay, when you get it, be sure to plug it in and check for PPV's left on it BEFORE you activate it on your account. If there are any, plug in a phone line, connect it to your dish (do a switch check of course) and go to the diagnostics menu (menu-6-3) and select phone connection. Then let is sit turned on for 24 hours, and check it again. If you activate it on your account with PPV charges still on the card, you will be responsible for paying for them.