This type of agreement is not litigation-proof, but you’re right that it can be an important tool. Unfortunately you can’t really just write up a contract that says “once we get your car all bets are off,” since those types of agreements are generally viewed as contracts of adhesion (too imbalanced in favor of 1 party) and often get tossed out in litigation (not to mention that judges get pissed seeing them). A limited liability agreement to at least cover JTech’s “diagnostic” period is in the works.