What is the ruling on a sheep seller refusing to hand it over to the buyer after the sale is complete, and then selling it to him again at a profit?

If the seller claims and proves excessive deception (ghabn fahish) according to mercantile custom, he has the option between rescinding the sale and recovering his merchandise while returning the price, or upholding the sale. If he chooses to rescind, the buyer is only entitled to the price he paid.

If the deception is not proven, the buyer has the right to take possession of the merchandise. The buyer can release the seller (i.e., agree to rescind the sale), and he may take more or less than the price paid. This is the more preponderant view, as the risk of usury (riba) in this case is remote, and this can be done through a new sale.

In summary: If the deception is proven, the buyer is only entitled to the price. If it is not proven, the buyer may release the seller for an amount exceeding the price, and this would constitute a new sale.