Here's a video that explains what a fitter is looking for when they do a bike fit.

http://activecitiesusa.com/?q=node/69

A friend of mine had a bike fit before she bought her bike. The shop charged $135 for the fitting but credited her $60 when she bought her bike from them. The shop also readjusted her old bike.

In some shops, if you buy a bike over a certain price range, the fitting is free.