Some general advise:
1. If the face is not visible the girls is probably not who you're going to get because let's face it without a face they can pretend to be anyone. The professional escorts I know in Prague have no problem showing you their face. If you contact them, ask for a picture of just their face, if they don't send you that or tell you some story about their privacy be careful! If you're going to pay two or even more times the amount of a standard private you should get exactly what you order so don't be modest about it.
2. There are many websites (and clubs to) offering massive amounts of ladies, they do this to get you interested in the hope that when you call or visit they can tell you the girl you want isn't available but they have an even better alternative. Be very careful with this cause this ends bad 9 out of 10. When you have a specific woman in mind make sure she's the one you're going to get, repeat often that if she's not the one who shows up you will not pay and should they send you another woman simply refuse her (but be careful in hotels cause you might not want to attract attention when a hooker starts banging on your door screaming her head of ;) The websites you mentioned don't look like much to me but then again I get most of my contacts from people I know, forums etc. Can't beat experience.
3. So how to get what you want? (I think was your question) First of all you made one good decisions you came here! This place is a goldmine of information, read the ladies profiles and look at the comments, visit some other boards like http://www.nornik.net/debata/viewforum.php?f=3 and others.
4. A lot of the women working in this business are Ukranians and Russians and service is not always good, English can be a problem sometimes because the woman you talk to to make the appointment is not always the one who ends up knocking on your door so make sure or be sorry.
Hope this helps, if you have more questions just ask :)