I've been using p411 for years, had to sign up twice after locking myself out of an old p4p email.
They want to know your home address, where you work, and your real name. There are lots of ways to establish these things, but they seem to typically request a combination of documents including utility bills, drivers licenses, pay stubs, and typically a discrete phone call to your office. If you have references from two providers active on p411 they bypass some of this.
They generally screen employment by calling the main line at your place of work and asking for you. As I understand it they're very discrete. However, lots of people work for companies without main lines or are freelancing/consulting/self-employed and they seem willing to work with you to prove your employment or source of income some other way. I believe I sent a pay stub when I was with a company that didn't have a central number.
Presumably they cross-reference this with Internet info (LinkedIn, google searches, public Facebook info) and also with public records databases to the extent available (at least for US users, almost everyone is verifiable with name, address, and date of birth).
I'd be somewhat surprised if they did a comprehensive criminal records check. That seems beyond the scope of what they advertise doing (verifying identity).
Basically, they're going to verify who you are somehow -- but are quite flexible as to how.
-- Modified on 2/24/2015 6:49:25 AM