I've never accepted a check for a used car, and I've never heard of anyone other than a dealer who does.
If you want a step by step for loading cards, there's a clear explanation at Million Mile Secrets, but in my experience as a car owner for way too many decades...don't expect a private individual to accept check for a used car. Maybe it's a regional thing but there's no way I'd take a piece of scribbled on paper in exchange for a car. If the guy has check, hey, I have the car, we can go to the bank right there and he can pull out the cash. You know? It's too much money to risk being scammed. Maybe if you're buying the car from a relative, this would work, but otherwise...I'm not seeing it.