Well, as no one seems to have posted yet about the opposite side - pro-spankees, I list myself as one of these, but *only* because I've been paid for the work. Just because I have a lot of experience, if I hadn't been paid for it, I wouldn't list myself as such.
For someone who *hasn't* been paid but still considers themselves a pro, I would expect that they could follow instructions given - things like staying still and quiet and actual *doing* it. I'd expect them to have experienced most common implements and positions. I'd also expect basic safety knowledge with meeting people, safe words