Pest Controllers are licensed through the state's Dept. of Food and Agriculture. NWCO's, if the state licenses them at all, will be regulated through the Division of Fisheries and Wildlife or Dept. of Natural Resources. Obviously, the first thing you should do is to look for a NWCO to handle your wildlife problem and not a pest controller. Once you know what you are looking for you should ask the following questions. This question is not to be confused with how many years in the Pest control business.
Bug killing is very different from controlling wildlife.
Too pest controllers start doing NWCO work with little to none trapping or wildlife experience. Find out if the person is licensed to do animal damage control work in the state you live in. While some states don't require licenses, many do. Ask if the person has completed a state certified trapping course. For the purposes of disclosure you should know that I am an assistant editor for the magazine.