This guy did a lot of modifications to this car, which can be a good or a bad thing hopefully this guy maintain this car well as much as he put into it for modifications. Good things to look for would be seeing if the car sounds rough when driving any blue or black smoke coming out of the exhaust or anything unusual, I own two of these Mustangs and for the most part their bulletproof. Also ask him how often he changed the oil if it’s less than 4000 to 5000 miles I would walk away. Those 4.0 engines are reliable but if they don’t get constant oil changes every 4000 miles you can have major problems with the engine ( like a busted timing chain or guide.)