I've always assumed that when WGs post the no black/asian/oriental thing it's basically three things:
1. They don't find them (as a group, generally speaking) attractive so it's harder to "work" with them. I don't find Thai girls attractive - it happens, get over it.
2. It's a way of trimming the customer base down without significantly damaging the earning potential. To say "no white guys" would be financial suicide.
3. They're racist. I've seen a WG a couple of times who openly says to me (as a white middle aged man) that she doesn't like minorities, full stop. She's an EDL, daily mail kinda girl
The whole "due to bad experiences" is a saafe-inspired piece of window dressing the pro$$ie thinks will justify the statement without leading to awkward questions from punters.
I also gotta ask: if you fall into the 'barred' category, why the fuck would you be interested in seeing said girl? There's plenty more skanks in the aw!