I've just done a search on Asian escorts in Northampton and of ten results I can say with some certainty that five of then are genuine. 50% on Viva Street is unusually high. Generally, if it says 'Thai' and has a name in the advert ( less reliable if it just says 'Thai' but gives no name ), they are probably genuine. Anything Japanese, or Korean, or quite a few of the Chinese, with what are obviously asian porn stars in the ad mean you will be taking a gamble over who you see.
By way of comparison, a similar search in Nottingham gets close on thirty results. Only three are likely advertising the girl you will see. Ironically, one of those is Chinese ( well reviewed on here - Yang Yang. However, her place has recently been raided and there are concerns over trafficking and also whilst the pic might be of Yang Yang it seems as though she might act more as a madame now than a service provider ) and another one is Thai but does not have a name in the ad. She does have the name Sara in the description and she has an a/work profile too. Add to this the photos, particularly the first one which looks like a studio used by a lot of the Thai girls who are genuine, and the reviews, and she genuine. The last one is someone who claims to be an Asian Colombian called Meghan. I haven't seen her and don't know of ay reviews, but the photos look like those taken by the same photographer as some of the Thai girls.
In Leicester and Nottingham, you can disgard about 90% of the ads on a regular basis if you are hoping to see the girl in the ad. Vivastreet can be useful but it is better if you keep an eye on it for a while to get a feel for which profiles are likely to be genuine and which ones are switch joints with constantly changing girls who aren't the girls in the ads and may, quite possibly, be trafficked.