A few years ago I looked at a Far Eastern contract that was being offered by 2 agencies; Rishworth was one and the other was from somewhere in Australia, sorry forgotten the name.
The contract from each was broadly the same except the Rishworth one paid about US$ 1500 to 2000 less.
I suspect the airline concerned paid the agencies roughly the same, but Rishworth took a larger cut.
Draw your own conclusions, but I'm not sure I'd knock on their door again. I'd always be left wondering......