I never endorsed or agreed with the non-refundable $200 deposit idea. I was expressing reluctance with the idea of letting a prospective buyer take the car to a mechanic.
OK, sorry. I lost track of who had said what.
In the UK, the situation is complicated by the insurance rules. Even if the potential buyer is fully insured, they will only be covered for third-party damage in the seller’s car.
That said, you can tell a lot about a car just by looking:
The general state of the bodywork
Damage to the upholstery is a big red flag
Any warning lights
Does everything work? - Lights, windows, power steering etc.
Under the “hood” are the fluids topped up and any signs of an oil leak.
Watch out for a nice new paint job. It’s probably covering lots of rust.