no reason to tell the LBS that you're buying online - you have to realize the guy is in business and probably has children to feed - all he probably heard was "I want a free fitting but you wont be getting a cent for the trouble."

just pay for a professional fitting ($100) and be on your way.

and if you're not willing to pay that amount, just use an online calculator.
the results are not as good as a in-personal professional fit, but it's free.