STDs: escorts and one night stands

[surferchick83]

so 2 questions related to the same issue:

Does anyone know whether all those legitimate ****** services are safe? As in, are all their models STD free?

Secondly, suppose you're having a pretty good time with a random girl, and there's a possibility that it could turn into a one night stand. How do you find out whether she has any STDs? Is there any polite/nonoffensive way to do it?

Thanks for all your advices!