I like to assist with references, but when a provider I've not met calls me out of the blue asking for me to verify that one of my customers is really a customer of mine I never know if I'm speaking to a real provider or the customer's wife's private investigator who's got his phone record.
If you can please have the customer call me first so I know he's really approving of the referral then I'm happy to cooperate.
Regarding P411, I've spoken about the ease of LE penetration in the past. Please be aware that there are LE as members of P411 and they easily obtain good references thereby. I know a well-known provider in Austin who worked for an agency here [still operating] which used P411 and aspd for screening. The client was in Round Rock and had both aspd and P411 memberships in good standing. When she showed up she was placed under arrest by the posing officer. She isn't one to solicit, so the arrest was probably illegal, but try explaining that to a Williamson County Judge near election time.
I've posted before about the misconceptions of screening practices I see used frequently in Austin, and her experience is a case in point.