If you need one of the services typically provided by a P.I. firm -- surveillance, locating a missing person, having a background search performed, etc. -- finding an investigator will not be a problem. There are 1,000s of them in business today. Some are experienced, well-qualified and ethical. Sadly, many are none of the above. Opt for an investigative agency with a website that is very clear in detailing their qualifications (ex-Federal Agents are generally considered to be the best of the best), their physical address (not just a P.O. box) and their license number. Regarding the latter, the private detective you hire should hold a license issued by the state, in good standing, and preferably with an origination date that goes back at least five years.