My experiences:
Seeking- too expensive really, girls quoting euro400 for hr/2hr meets, plus at least one chancer trying to charge high for platonic meet. But only place for Serbian local girls though as was very tempted by one but in end felt that the price was too high. They're all transactional about it too - In UK seeking can be more of a dating site, and I've had a couple of freebies with fit girls in their early 20s from it (although date drinks and food etc cost was at least £100 each time) when you put time into building a connection, but in Serbia it seems just like a site for high end escorts and no one is interested in anything less transactional.
Agencies - some didn't reply. One called Cat Agency did and had fairly accurate photos and videos of their girls, one Belorussian girl was really good service, another Ukrainian girl was awful. Pricing was a little high compared with london, at 200eur/hour incall or 150 for 30 mins.