The definition of a pro is someone who makes a living by virtue of what they do. A plumber plumbs, a carpenter pounds nails and saws wood, and a stereo dealer sells and sometimes installs stereo equipment.
They get paid to do a specific job.
How good they are at that job should in theory determine whether or not they remain able to support themselves over the long term. In our capitalist system, the idea is the marketplace sorts out who's good and who's not.
That model's fine in theory.
Fortunately, we can often judge a pro by their work. The pipes don't leak, the house doesn't fall down, and your stereo system brings you more pleasure than you had hoped for.
On rare occasions, we get to watch a master practice their craft: John Hunter or Peter McGraff setting up a stereo system would to me qualify as true masters of their craft.
Whatever level of pro you might be considering help you choose your stereo gear or set up your system, the best advice I can offer is to first make sure your values line up with theirs. Do they have experience helping others get to where you wish to go?
Once you've managed to form a bond of mutual values, pros can offer a great partnership.