trust, trust and more trust... take your time to listen to what the tuner says, look and research his previous work with your own eyes if poss and get everything in writing just in case if poss anyway.
In my case, ever since i met steve scott i had complete faith in his ability and his honesty. okay so he might shoot me now and again with a gas powered bb pistol or a compressed gas powered tennis ball gun but that's a small price to pay IMO... i trust him 100%.
Ben