"I'm going to compete with eBay in a market visibly riddled with fraud and malicious actors" is probably a bad omen regardless of the third-party problem.
But. If you arrange the transaction between the two sellers and hold payment+device in escrow, then that's clearly "arranged between two sellers" and wouldn't be the target of this ruling.
(Escrow insurance isn't cheap, though. And without escrow, you have nothing but risk.)