I prefer to prescreen! The trick is to make sure and not flake on the date!
There have been clients who book with me up to two weeks in advance and I really appreciate that! Typically, the p411 guys are the most trustworthy because they pay to keep their profile updated and are more serious about the hobby, usually travelers. Not to say that eccie guys don't keep their word...
My favorite approach is a guy who will politely introduce himself and what he is looking for. Has already researched me and knows not to ask stupid questions like how much is your donation(every Provider's biggest pet peeve)!
Books for two+ hours with plans to share a bottle of wine and some conversation before hitting the sheets!
I have defiantly had some outstanding dates from these sites! I love meeting new people and learning new things from clients.