Since lots of building conditions can cause odors (ranging from dead animals to sewer backups) and since some of them can be tough to track down (sun-heated plastic windows, window screens, or vinyl siding), also take a look at the links along the left of this page....
Doing this yourself insures that the goon at the tint shop doesn't just tint over the old stuff (lots of factory tint is almost invisible) and increase your chances for bubbling. Also, it will save you the expense of the shop charging you to remove it, and potentially not getting all ...