I think it's totally normal to research a therapist before you call them. I would assume most therapists would expect that you might, and that's one of the reasons for having a LinkedIn profile in the first place. (It sounds like maybe you don't use LinkedIn much? People check out professional acquaintances all the time on it. If you use it a bit you don't give it a second thought when you see someone has looked up your profile.)

I read my therapist's book before I saw him, and I told him I had done that. He seemed to think it was a totally normal thing to do.