It usually takes at least 5 genuine-looking feedbacks for me to feel even vaguely confident. However, I do love seeing girls who've yet to become jaded by their choice of career, so I've been known to book 0 feedback girls on occasion. It's a risk, and sometimes I've been disappointed, but I've been lucky enough never to get seriously fucked over, and sometimes I've struck gold.
Quite why you'd pay £200 for the girl you've linked to is another matter. Each to their own and all, but what on Earth is so attractive about her that she's worth so much more to you than the legions of cheaper, younger, prettier girls out there?