This is like blind man's bluff. Is the bike fully Shimano 600 equipped? Did the shop make any claims as to how they serviced each of the bearings (headset, bottom bracket, hubs, pedals)? Were the cable housings replaced with modern lined housing? Are the tires new? Is the chain new? Brake pads new? If yes to all of these...then you only paid $100 above full market value.
In exchange, you got competent servicing (assumed), a bike that will be trouble free to start out, and one that fit you. You didn't have to diagnose and do any of the mechanical work. I'd say that you did fine. Ride it.
Also, post photos and answer my questions above. PG