Very thorough!! Walked me through step by step of the problems associated with the vehicle I was interested in purchasing. His knowledge on different car models shows greatly as well as his experience. He informed me about a thumping noise that the engine makes upon start and warned me to be cautious of it. He advised to not purchase the car if the dealership does not handle the problem. His advice is solid and he gives me confidence in negotiating prices after pointing out other problem areas on the car. Mark is awesome!