Setting: Modern USA (or UK if you happen to know)
Character A has moved towns/states and cut off all ties with his family, who are intolerant of his lifestyle (insert gay/hippy/superhero as appropriate - he is not, however, doing anything illegal) to the point of harrassment. They don't have his number, his address, or know where in the country he is. He's also left behind most of his friends, but stays in touch with a few he can trust (and who know full well that his family is crazy). Apart from that, he's not trying assume a new identity - he's using his college degree and trusted references from his hometown to get a job.
If a member of the family hires a private investigator to find him, will the PI take any steps to check up on their motives? Is she obliged to? If she does, but they tell her a sob story about an argument that got out of hand, or a misunderstanding, and demonstrate their loving family environment, would she be content with that? If, on investigating Character A, she spots the big discrepancy in lifestyle, would it occur to her that the family's interests might not be benign, or would she simply "do the job" without thinking about/caring about consequences? What if she talks to one of the friends and they tell her flat-out that the family is crazy and that A wants nothing to do with them?
Character B has moved towns/states and cut off all ties with her partner due to domestic violence. She has never brought charges - maybe she's just scared, or maybe the partner is buddies with the local police, or maybe even her own family doesn't believe her. She has made considerable efforts to hide her trail, to the point of faking documents to get a job. There is a good chance the partner will kill her if he finds her.
Similarly, if he hires a PI, and tells her how they had this argument, and Character B ran off, and he's really worried about her because she's never been gone this long, does the PI simply take the job, no questions asked? If she hands over all the details the partner needs, and he then goes and murders Character B, will the PI be punishable under law for providing that information, or will she be able to hold up her hands and declare she had no idea it would be used in that means?
What I'm getting at here is that I have this idea that PIs are not subject to any restrictions other than their own moral code - obviously they can't actively break the law, but I've seen a number of websites cheerfully advertising the ability to provide someone's address, phone number, job description, etc, and it gives me the chills. I would like to know how strictly enforced the codes of ethics are, whether or not the average PI gives a damn about what the information is to be used for, and whether there are any legal repercussions for turning a blind eye. I appreciate that many PIs are presumably ethical people who would make the effort to check up on their client as well as the subject of the invesigation, but I want to know if there are any checks in place to counter the ones who are perhaps less scrupulous.
Related: once the PI has entered into a contract with someone, what happens if they turn around and say "Actually, I don't want to give you these details"?
Once again, this is modern USA - I'm not interested in what Philip Marlowe would do. ;)
Search terms tried: private investigator ethics, private investigator law, private investigator domestic abuse - I've also visited a number of PI agency websites, and searched this comm and checked tags