One of the things that customers seldom understand is that PI's cannot do everything they want. OK, maybe they CAN do it, but they shouldn't do it. If you are considering hiring a private investigator, ask yourself "What do I want out of this".
You need to know what you expect. A good private detective will explain to potential clients what they can and cannot do in a case. The largest complaints against PIs are not about doing inappropriate things, but about not fulfilling expectations.
The accomplished PI will ask enough questions to know what the client wants and expects, and then explain what the PI can and cannot do.
Most people are reasonable. Even emotionally charged clients who have been cheated. If the private investigator takes the time to ask enough questions, and then explain what they can legally do, the clients usually understand what can be accomplished. Often clients expect to get graphic photos or videos of a cheating spouse. Unless the cheating is going on in a parking garage, that is very unlikely.
What can be documented is arrival at the same place and time possible on multiple occasions of two people who have no other reason to be together other than an illicit affair.
Most cases like this are circumstantial. Rarely is there photo or video evidence of the dirty act. However, when the cheater is presented with evidence, they often cop to the cheating.
I hope this helps -
Whatever you do, Stay Safe!