It's done by the lady...  after she sees you.  Some do but in my experience most do not.  I got 1 without ever asking.
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their criteria for white listing varies from provider to provider (hotly debates issue) but its a personal "vouch" so a good guess is clients they are sure are safe would have a better shot at being white listed.

Some ladies do and some don't.  Those that don't have several reasons.  (1) You may have been a gentleman with them but if you change your ways, their cred goes downhill  (2)  Could be used to verify that the date did take place.

For reason #2, I have stopped asking ladies to be white listed.