Buying a used car is the biggest purchase most people make without an expert in the room. The seller knows the car's history; you know what it looked like for fifteen minutes. A mobile pre-purchase inspection evens that out: a mechanic meets you at the dealership, the private seller's driveway or the parking lot where you're meeting, and inspects the car before you commit.
Mobile is the only practical way to do this. The seller isn't going to let you drive the car to your mechanic across town, and dealers rarely have time for it. A mobile mechanic who comes to the car removes the friction, and the inspection usually takes about an hour.
Mobile-Car-Repair.xyz has a local mechanic in 250 cities doing pre-purchase inspections. Reach out through your city page before you negotiate, because what the inspection finds is leverage.