I knew a guy who runs (ran now maybe) a back alley shop the people in the hood would take their stuff to. He had an account at a parts store. One deal he liked to pull, customer would bring their car in for a no start. Shop guy would diagnose it, maybe it would need a fuel pump. Shop guy calls the parts store, verifies price and availability and says to bill it to him and the customer will come get it and pay for it.

Customer retrieves and pays for new pump ($3-400 usually) and takes it back to the shop. Shop guy tells the customer that he'll call him when it's done.

Shop guy will go to the junk yard and buy a fuel pump or whatever he needed to get the car going. 10 or 20 bucks. Put the used fuel pump in the car and get it going. Bring the new pump back to the store with his receipt, tell them he didn't need it and get his 3 or $400 back. Cash. Did that all the time with all kinds of parts.

It's a jungle out there.