How do providers/agencies screen? Who do they call, what information is needed and how is this done discreetly?
Thanks in advance!

For example, they can look up your address and phone number to make sure that they are real.

They might call where you work and say something like they need to send you an email and ask for same, or check the spelling of your name.  These generally don't arouse any suspicion with the front office.

The most common way of screening is to check with other providers you have seen.  Most gals are willing to offer this as a courtesy to each other and the client, but good manners dictates that you will always let the gal being listed as a reference  know that you have done so, so that when the provider you want to see calls her, she will be aware of this.

like Date Check, Preferred 411 or Room Service 2000.