I've dealt with a number of P.I.s, process servers, and related people in the past 7 years. I'm more than qualified to comment on this sector.
If you're an individual, and not a corporation, and you hire a P.I. who isn't a retired police officer, the odds are high that the P.I. is going to overcharge you, lie to you, or steal from you. If you ask questions, the P.I. may threaten to sue you or to have you killed.
I've been through all of this. Amazingly, much of what the P.I.s have said to me is in writing. Over time, I'm going to post their names, their State license numbers, their false statements, their threats, and my assessments.
I'll include the FBI report that I filed on the P.I. who suggested that he could have me killed.
I'll comment on good P.I.s as well as bad ones. There are a few good guys out there. Not like Magnum, P.I., but polite and trustworthy.
One take-away is that retired police officers might be a good bet. However, most of them prefer mundane cases. They're hoping for a quiet retirement. They aren't seeking Magnum, P.I. cases.