Come on.
Asking someone to become a member here? Seriously? You want to count that as screening?
Please go read that thread about how the ASPD social got hit by ASPD members who were in fact vice officers and roughly a dozen folks were arrested and one provider even got deported because of her arrest.
Pretty sure that you will read that the undercover men and providers were members with posting and review histories. If you look for Hambone's post in Houston ECCIE Discussions, you'll see a long winded multi-page discussion on the issue.
Force or request them to join P411?
Again, good luck.
Anyone who thinks that the police, who routinely create fake identities and work histories for undercover offices to infiltrate criminal organizations can't get on P411 is either living in a a fairy tale land or is in need of a wake up call. Go run a Public Data search on an undercover cop profile and you can bet your ass it will come up clean.
So what is left for your screening?
Call a provider a handle has reviewed? Better hope she has a great memory.
Anyone can pay for a month's access and WHAM, they have enough details to create fake reviews and post on and on. How many escorts over the years have created client handles and posted reviews on ASPD or now ECCIE simply to look at men only areas and data.
The single most important vouch I have ever used is vouching a select few guys I know and have known personally for many years. That list is small. I have known them for years. I personally think a vouch from a close friend who you have already seen is much safer and smarter than from some provider who sees numerous clients a week and if you were to actually ask them to physically describe their last ten clients couldn't tell you didly about them. Providers tend to remember the bad clients. Rarely the "average" joes out there.
If you're concerned, meet him and his friend someplace for lunch. There is nothing illegal about meeting for lunch. (Think socials) and then you can talk to the new potential client face to face.