That's a great question; it has been asked and answered before, but it is a popular topic, so here goes...
First, I want to clear up a common misconception: KT is owned by PeruTops, but it not in any way an agency for the girls. KT is solely an advertising page (or "Escort Mall") where anyone can buy advertising space. It is a good advertising vehicle, due to the site's close association with its parent site, but KinesTops status as an 'operation' starts and ends with the ad you see when you click on the girls' thumbnails.
Many of the girls' ads on Kines tops have a 'seal' that says Sello de Garantia. Basically, what that means is that a member of the KinesTops staff met the girl somewhere and took her picture. I know this for a fact, because I had the opportunity to be the 'oil boy' on one photo shoot.
The guarantee, basically, is that yes, this is an actual girl, and yes, she is the one in the ad.
The girl can either be independent or work for an agency. There is nothing in the ad to indicate her status. A search of the phone number in the Kines (Spanish) section of PeruTops may be of some help... maybe not.
If she is independent, there is a good chance that she will be the girl at your door, but there's nothing to stop her from farming out the call to a friend.
If it is an agency ad, there's the possibility that the agency will send over whoever they want to, but if your Spanish is good enough, you can firmly explain that you want the girl in the ad, and no one else.
Photos without the 'seal' have been provided by either the girl herself or the agency, depending on the girl's employment status. They can either be existing photos that the advertiser already had, or they can be total fantasy. Again, your Spanish phone skills will help determine that.
All that being said, in all of my times when the girl at my door was not the girl in the ad, I have only had two bad experiences.
I realize that this may not inspire tons of confidence, but that's the big picture, as I see it. Maybe others have different opinions; I would love to hear them.