Each TV depending on the make and model has settings that are best suited to it, and each person has their own preference.
Personally I wouldn't let the Sky Techs tune my TV. I'd check the forums for users who have had success with settings for the same TV as yours and "suck it and see" or if you're serious get a Visual/Audio specialist as you mention in that has the appropriate skills and tools but not the Sky tech.
My 2 cents worth anyway.