You can perhaps collect negative experiences from people you trust, and use that to narrow your selection. But you can't use good experiences, since the treatment people were happy with might as well have been a no-op and whatever problem they have would have gone away by itself in a short time. And if there wasn't a noticable pre-existing problem that was treated, but something the dentist made up on the stop, the treament someone was happy with might as well have been actively harmful, just not enough to be noticed right away.

Dentistry simply have too little credibility as a profession. If you need to pull a tooth out to make it stop hurting, sure, a random dentist is quite likely to do a reasonable job. At least compared to a random blacksmith. But as countless articles linked in this thread shows, dentists have absolutely no clue if you have cavities that need to be treated.