I can go and take the car off his property? Like a self repo?
Yes, you CAN legally repossess YOUR vehicle.
You should NOT trespass on or over private property to do so.
For example, you could DISCRETELY follow the vehicle to a Walmart parking lot.
You watch the occupants of your car park and exit it.
You might slowly take 60 seconds to make your way to your parked car.
You COULD simply unlock the vehicle, start it, and drive away to parts unknown.
Once you've recovered the car, contact the local police about what you did.
Be sure to have proof of ownership and insurance with you.
No insurance?
Place the vehicle on a tow dolly.
You're going to have to do a great deal of work to obtain a car worth less than $500 to a CASH buyer.
You might wish to THINK this through before taking any actions.
The lesson here is as old as time, don't hand over the merchandise until you have ALL of sales price in CASH in your hands!!!!!