First, we could never get our money back from insurance. The dentist would make you pay the entire amount up front, then the insurance would send money to the dentist instead of back to us. As our old dentist only "signed checks once a month," according to his lovely receptionist, it would sometimes take us three or four months to get refunded. (The receptionist quit a couple of years later, saying she couldn't stand working for him anymore.)
But the straw that broke the camel's back... our old dentist took his prescription bottle for some medication back to the pharmacy to get it refilled. Only, he'd forgotten to take his COCAINE out of the bottle before he turned it in.
We got a new dentist.