I look at this from a shop manager's point of view. I ask that you bring it back for us to look at even if it is a simple turn of the barrel adjuster. We record in our computer that you brought your bike back for a warranty check. We can add comments as to what we actually did to the bike. If six months down the line, you bring the bike back and report that it has always not shifted correctly, then I can pull your service history back up to see what service has been done on the bike (paper trail).

inatree - On another note, did you know of your shop's poor service reputation before purchasing your bike?