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.
2011 E92 M3 DCT
1991 Spec Miata
2008 E92 M3 DCT - KW Competition 2-way / Brembo 365 BBK / OMP ARS racing seats / rear seats delete / GT4 aero / AiM EVO4 data logger / SmartyCam racing camera
2008 E92 M3 6MT
2008 E92 335xi