If they didn't charge you, and you're comfortable with the service, then all obligations have been met.
Originally Posted by calnalu
And there's certainly nothing wrong with giving a high-end estimate and coming in lower. It's what I've always done when working with projects billed hourly. And it's entirely possible that if it had stayed for more work, a "level 2" (as we say in IT) technician would have looked at the tach and spotted the potential issue immediately. SFBMW is a big shop and presumably has a large service staff with a variety of experience levels.