Look in the yellow pages under Pest Control for a licensed, bonded and insured company, or get a referral from a local real estate agent.
Call several companies and get a quote for the cost of inspecting the home.
Compare rates. If you are just having an inspection for the purpose of buying or selling a home, the cost shouldn't vary too much. If you want a monthly pest control service, find out what guarantees the company gives if an infestation returns before the next service call.
Request a copy of work done and clearance before signing any real estate papers.