for dentists as for outsourcing, it is often an unnecessary effort to try to find the best available one. "he's okay" is a perfectly fine metric - i.e. "will do the job i need done, at a price and quality that are acceptable to me". small-scale yes/no-based reputation is fine for that.

more specifically, you don't need your neighbour to have seen lots of dentists so much as you need lots of your neighbours to have seen joe on maple street and deemed him okay.