LBS here offers 6 months of Free after the sale service on all new bikes sold. the tune up is part of that service .

But that is a Management choice of the Individual dealer ..

If you buy a Bikes Direct or Big Box chainStore sold bike, they have no service people, but you did get to pay Less. initially..

if you made errors in your DIY assembly perhaps the skills are not there Yet.

I'm not there to judge.. if in doubt having a shop mechanic check over your work, is a good idea .

new hire mechanic's assembly work is checked by a second mechanic, at my Local ...