The cheap agencies who appear too good to be true generally are too good to be true.
For example, a quoted outcall rate of £80 is accurate, but think of that as her travel costs only + a cum-once, basic service.
Also, when the girl arrives, expect to pay more for each and every service in which you wish to partake.
"OWO, that's £20. CIM, that's another £30. Facial? Sure, £20 more. Anal? Yes, I do - for an extra £50" ... and so on.