Put it this way: I take my rims down to the tyre shop in my daily driver, get the tyres mounted while I watch them while they mount the tyres (despite this I have already had a prybar put through one of my wheel sensors ;30), take them home and mount them myself.
When I first had my car I realised the rattle guns these tyre places use do not work well with GM lug nuts & studs after having to replace about four seperate studs & nuts. Now I torque them up to spec with a torque wrench.
Too much chance of someone with no idea putting a jack under a fuel or brake line, fibreglass leaf spring or (god forbid) your fibreglass floor). Personally after some of the things I have seen I prefer to do as much as I can myself.