That's what you said non-operable , did the car start and drive when you drop it off? Now what they did after you left you don't know, Sorry to say but it sounds like they took it for a joy ride and hurt the motor.
You are a an expert huh! Bro no offense!. My friend is trying to solve his problem, and not alone listen to you with negative comments! Either make your point on the problem, and less on your negativity! You must work for Kenny? Right!