A provider you see who is a ter member you can ask her if she will whitelist you after your appt.
Some providers will do this and some require you see them more than once.
You mentioned another site ok I guess you are referring to P411 a provider giving an ok.
The difference between whitelists and P411 ok is that P411 is a verification site and TER is a review site.
Some ladies will accept whitelists and P411 ok and some want more info besides just a whitelist or P411 ok.

Here is the link to the info regarding whitelists posted here on TER:

http://www.theeroticreview.com/info_policies/whiteListFAQ.as

I am wary of whitelist referrals, because this is a review site. The conflict of interest is inherent.  

If a reviewer is asking for a referral, I'd assume that I'd garner a bad review or bad backchannel if I refuse... so I just cave in, whether or not the client is truly deserving of my good word, or not. (Of course, if he was truly dangerous or behaved very egregiously, I'd refuse.)

Most clients to whom I've given whitelist referrals asked for them.  I didn't volunteer... and for the most part I wasn't entirely happy to give it. In fact, I just recently gave a WL referral to a client to whom I refused a second appointment (he was very safe, just a HORRIBLE pain in the ass with deplorable hygiene).  

Most of the clients who expect me to screen them solely though whitelists have many issues that would make me less than eager to see them... IF I did accept a WL as screening, I'd treat it the in same manner as a reference or a p411 OK (I'd double-check with the referring provider). But for the most part, those clients express themselves so crudely that I'm only too glad to say to them 'I don't accept whitelists as screening, sorry!'

When someone tells me that he wants to be screened solely through his WL's... rightly or wrongly, it says to me 'If I give an actual reference, the lady might say something bad about me. But she gave me an OK here because she knows I'm a BMOT (Big Man On TER).'