There's nothing to stop you from claiming the account was stolen and getting it right back.
I know. Is there any other way I can sell an Origin account so I can't claim it back?
None that I am aware of. If you can prove original purchase, they'll give you the account back every time.
You could always rent it out. In effect, say "I will guarantee this account for a year" while agreeing to keep the money in escrow the whole time. Then again, the buyer could simply play on it for nearly a year, claim that the account has been taken back, and try to get the escrow money back that way.
There's not really a good solution for selling accounts online.