Apparently you posted this on Another board and admin moved it here to the newbie board. This is the proper board for questions like this, but if you don’t know they moved the post, you may not even find it.
If you do make it back here, I suggest reading the self help manual (TER instruction manual) at the top of the page for a lot of general guidelines.
As to screening, you have to find what works for you and what makes you feel most comfortable. There are different ways to screen, and many providers use multiple methods. As querty mentioned, some providers ask for real world info from the client (real name, job info, etc.), And some clients gladly give that info, however many clients will not give up any real world info, and you have to decide if that is something you will require or if you are able to screen by other methods. Many providers use references from other providers. There are also screening sites like p411 (mentioned by inicky earlier) and provider only sites, blacklist sites and even google. While p411 can be a good screening site, you can’t just “join” p411. You need to be “invited” by client members. (As mentioned by Lester above).
Honestly it is better to discuss screening methods by back channel (email or Private message) and not on a public board.
Hopefully a provider (like Debra Hollander) will see this post and give you some advice.
Good luck and come back to the newbie board any time for more questions.