Professional shops will be professional. Service $'s are the best kind usually, much better than selling stuff (except stuff like tubes, levers, and patch kits which usually are marked up 300-400%).

If you go in with the attitude that they are trying to screw you and do shoddy work then they may pick up on it and treat you accordingly.

My shop would probably charge you ~$30 to adjust and ensure things are good. This would include a wheel true (not tension). Most knowledgeable wrenches could check safety on your bike in < 5 min, and since there are no gears to adjust, there is less to fiddle with. Checking torque on your bolts, play in your bearings, wheel true another 10 min....

Glad you are having someone who knows what they are doing look at your bike, as even their half ass is still likely better than your whole ass.