For us old timers who are used to dealing with the "professional" ladies here, we just assume that there is cooperation amongst all of the ladies.
Unfortunately some women just feel "threatened" or like there's competition. I found this to be the case more in Vancouver, where screening is almost nil. Some women will either give bad references (for a good client), no reference at all, or good references for bad clients.
Two "upscale" providers were assaulted (by the same
white client), a former provider was murdered, and two girls from a local micro (AMP run out of a house) were murdered that year. So I started the reference ribbon campaign (
http://missy-mariposa.com/reference.htm) which I was hoping would at least help out a bit. It did, at least in my eyes. Now I see that banner everywhere, which makes me smile too. All I ever wanted was women to feel safe asking another woman for help. And for women to be safe at work. Not so much to ask really.
As far as your problem OP, I don't know what to suggest. I offer similar screening to you - P411/DC, References, and Employment Verification. If a visitor is in the military, there are a few other ways you can screen them to prove that. I've seen university students without jobs, as there are also some easy ways to verify them. But other than that? No exceptions.