It will take a couple of Hundred miles for cables to stretch or the wheels to show any spokes out of line. Unless you have a computer that shows the milage- How is the shop going to know the milage you have done?

It is a good idea to get the "Free" Check up done but If the gears are causing a problem- or a wheel is out of true- or there is a sqeak coming from the pedals- Tell the shop when you take it in-