You don't really service a gun,you clean it,and if it breaks[vary rare thing in my opinion],you either,send it back to manufactor for repairs,or you take it to any gun repair type person[who might want to,or in most cases,able to,work on it].
A gun shop,for example, will put a scope on for you and bore sight it for you,even if you didn't buy gun from them,bet most will do it even if you didn't buy the scope from them,money is money.
Gunsmith,thats the word I was searching for!
Thing about a good gun shop over walmart,is hopefully they can answer your questions if you need questions answered that is,I never needed to ask them what to buy,already knew that,but some do need info,so for somebody who doesn't know what they want,or doesn't know the difference between a 30-30 and a 30-06,than yeah gunshop would be better than walmart.