Competence, professionalism, attitude, price.
I like GP's service department, bike sales (bought a Ducati from Gini, and the year prior Carl never called me back when I asked him to get me a new KTM so I ordered one from Ottawa dealer two days later), and parts departments and use often. I often avoid their gear/accessories dept though as 9/10 time I'll get someone with a cocky/poor attitude (Marianne is awesome though).
When I had a Victory I dealt with Spoiled Sports and while their mechanic was awesome their parts/acc people are incompetent and have bad attitudes so I would ride 1hr farther away to deal with Deerhaven which are excellent.