It's ok Geyser - doubt his expertise. Someone who "looks at you", has you sit on a bike for a brief period of time and then tells you the frame size you need, is just guessing. Any good LBS will give you a bike fit and they should do it without charging you if you're having it done in order to buy a bike. Especially a higher end bike. I would either find another bike shop or find someone else at that LBS that inspires more confidence in you.
After all, you won't ride a bike that doesn't fit AND....it's YOUR money! 
PS: there's a thread under open titled "getting to know you". Gives you a chance to learn more about us and tell us more about you!! and welcome to the board!
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"