$500 is crazy lol
I wonder the same when I see the prices for Chinese privates like MOC and Sydcolour where the girls range from 500-800/hour but offer even less services than 300/h girls at the shops. What I gather from catchgod (that gets translated properly anyway) is that alot of the Chinese punters don't care much for service and prefer the girl to be (or at least look) young and look hot. And are willing to pay that premium.
Same for Jess, probably - she seems to work only 2-4 hours per shift, and I'll bet they are guys who have seen her regularly, and are willing to put up with the higher price to be exclusive.
There are people here who are flexing they tip girls extra for nothing in return, so yeah, it's not about the girl's supposed worth - some guys just have too much money and no sense.