Were they actually working on the tire for 4 hours or was that how long it took from the time you got there till they finished? And what damage could they have done changing a tire? Was it a front tire or a rear inside dual? Makes a difference how long it takes. Was it a tire they had in stock or did they have to go and get one? Did you have an appointment or were you a walk in? Personally, 4 hours doesn't sound too bad to me, especially if they had other customers, since I doubt you had scheduled a flat tire, those things usually happen unexpectedly.