Is buying and selling a car considered usurious (ribawi) if the car was bought in installments from a person claiming to be a guardian of orphans, and the latter bought it in cash without seeing it?

If the car is described in a way that eliminates any ambiguity about it, then the first sale is valid; otherwise, it is void. As for the second sale, it is void in all cases, because it is impermissible to sell a commodity before taking possession of it, regardless of whether the first contract was valid or void. Furthermore, the second sale is also void if it was an agreement for an usurious loan.