I’m not going to address individual posts because there are too many of them, but if you structure the sale so that if the buyer doesn’t pay it reverts then retroactively you owned chometz on Pesach. That is not the way it should be done, and not the way I have seen it done.
The sale is a 100% sale, and ideally should be structured so that even if the buyer never pays the chometz is still his, and he can be sued for the money. That is the way every sale I’ve witnessed has been done. And no, there is no guarantee that we will buy it back, but we can give him an informal assurance that if he doesn’t find a buyer in the next week we will find him one.
In the case of individual householders, of course we want to buy our former chometz back, because it would be inconvenient to have to go shopping to replace it. But in the case of a business, on the contrary, we would be delighted if he decided to take it all and pay for it.
The reason we buy it back is very simple — if we don’t, then next year we will not be able to find a goy willing to buy it from us.