I've never employed a private investigator and I think this is a good thing because I associate them with personal or professional problems so it's better to be far from these situations.
I hope that I've never had any experiences with one of them but if I'm wrong perhaps it's because he/she was very good doing his/her job.
I believe this kind of job is necessary in our actual society but I prefer not to get a job like these basically because I'm not interesting at all about other people's life.
Really I've just worked in a few number of diferents jobs and any of them were really interesting or strange. Perhaps my actual job working with the Catalan police is the nearest job that someone could call different.