Since most tuners are not going to show or tell you the details of their tune, you best bet would be to base it on their experience and track record (this is from LBM). In other words, go to a turner who has a history of well-executed tunes.
Avoid inexperienced tuners. It takes a lot of experience and technical know-how to properly tune an ECU (meaning unleashing performance while maintaining judicious safety margins, driveability, maintainability, emissions, etc.), especially on a car like ours which has a very advanced control system.