Nah, don't worry about it. I don't personally know any other proxy shoppers at all. I'm aware that a few advertise on doujin_market like I do, but I don't know what their service is like. (I think akino_djpick ran services for some of the big events, but I have no idea if they're still active, or anything about quality or cs.)

I'm assuming that the circles you're interested in do not sell their books outside of events?