Hi gavra-at-work.
Exactly what point?
You WOULD hire a private investigator to check on the person?
At this point I think you backed yourself into a corner, and on a topic that is not a light weight one.
As a reminder, the thread is discussing someone who “senses” the one seeking tzedaka does not have a genuine need.
In light of a rabbinic quote, statements from the Aruch HaShulchan, with all due respect, where exactly DO YOU draw the line when YOU “sense” someone is not genuinely needy? And, what makes you “sense” they are not needy?
You dont have to give a specific answer since most of us follow the Jewish perspective.