If you have a PPO or Indemnity Plan: Since these are plans where you can go outside of network or choose your own dentist the insurance company is out of the lope. Even though a dentist may call on coverages, it is up to you to make sure you are covered. You can do this by submitting a quote only to the claims department before the work is started or you can call. Many PPOs or Indemnity Plans pay based on % up to ACV/UCR so even though you may have coverage if your dentist is above the ACV/UCR you can get hit by a big bill. (that is why I advise to submit claims as quotes before the work is started. This helps you know what is your true cost for any procedure)
If you have an HMO: HMOs are different in that you have to go with their providers. Cost for procedures are normally fee based. Meaning that the dentist will charge based on the fees laid out to them under the plan. Therefore if you feel your dentist lied to you about your coverage I would start by calling the insurance company. Telling them what you had done (need ADA codes) and finding out your true cost. If they did a procedure that was not covered and told you it was then at least the insurance company will then be aware of this. They do not want their dentist doing such stuff to their Insured and to many complaints will have them removed from the program.
There is as you menshion the better business, but there is also the America Dentist Asso. ADA. Most states have there own ADA web site.
You can also find web sites that you can leave a blogs about the dentist you went to this will help others in not going to them. I sell dental insurance and dental plans so I have clients that tell me they google,yahoo, bing ect the dental office before choosing a dentist. I am just not sure how much effort you want to put into this.