Concerning the S/C belt... exactly what Wyatt said. There's a belt tension testing tool that costs a few hundred dollars. It's very doubtful that many dealerships even have that. They just make it "tight enough". You should order the TRD dynamic belt tensioner and have them install it at the same time. I had the S/C belt tensioner installed about a year ago and love it. It greatly simplifies changing the belt yourself too.

Jeff
2000 4Runner SR5, supercharger, rear e-locker, ARB front locker, 285/75R16 MT/R's, custom bumpers & skids
2007 Tacoma double cab 4x4 - stock