I tell them I want to take it for a test drive and have it inspected by my mechanic. They should not have a problem with this as they will have a copy of your driver's license in the event anything is damaged. If they refuse, I tell them I must be allowed to do this to ensure there's not any defects in the vehicle or I'll purchase from another location. Never had an issue with that. I've had multiple cars with cracked engines, bad transmissions and almost completely failing ball bearings. the $20 inspection is nothing compared to the costs for those repairs.

Never pay the price they have, always haggle for less. The most important rule is to always have a mechanic, who is not connect to the person or company so a full vehicle inspection. If they find anything, require the person or company to either fix it or subtract the repair cost from the price. Show them the estimate for repair. This has saved me thousands of dollars