No, I had never need a private investigator, but long time ago, my aunt need one to investigate her husband who she thought were having an adventure with another girl. She paid for that and after some time, not more than 3 weeks, she discovered de truth, and the sad truth because the investigator confirmed her that her suspicions were real and that her husband was having a extramarital adventure.
I wouldn’t like to work as a private investigator, I think that is a very compromised job, because normally the people contract this services when they have problems and the investigator normally have to give bad news for one or for another part. I think you have to have a special qualities to do this kind of jobs.