You made the rov a shliach to sell the chometz, and to buy it back after Pesach if it’s still available. If you don’t want to take possession of it you don’t have to, but you’re not getting any money.
Neville & Ubiquitin, first of all the repurchases I’ve seen absolutely were exactly that, the rov explicitly offered to buy the chometz and the goy agreed to sell, and they did all the kinyonim. But according to you, how is it that the goy walks away with a profit? How could he make a profit if he didn’t sell anything? If he is simply allowed to back out of the original purchase then he should be lucky to walk away without a loss? And yet he must make a profit, or else why would he agree to participate in this whole rigmarole in the first place?
This proves that what is happening is a genuine sale, followed by a genuine resale at a profit. The goy buys it in the first place, not for his own use but in the hope of flipping it at a profit. A week later he has not yet found a buyer, so we offer to be that buyer. That is all.