I have a rule at my home...until I clear someone they are not allowed to come and go, period. No new names and faces. It made my kids crazy but they were not the best judges of character. They proved this time and again until at least their mid 20's.
Oh, he is a friend of a buddy of mine. BS.....And your situation is the reason I had and still have this rule.
Yeah, it is the "friend of a friend" that will, most likely, rob you. You have a good plan going there.
Besides not talking too much about my stuff, I have a habit of not naming names when I talk about something a friend owns. I never even mention a first name or where they live. All I will say is "A friend has one of those and I shot it." or whatever. No names; no locations.