Free market capitalism. One of the things that made America great.
They can charge what they want until people stop buying.
That comment on the Forbes 400 is particularly telling and "in your face." Kinda like "if you can't afford us it doesn't really matter. Go suck eggs."
I've never bought from them and don't plan to ever do so.
For the record, when I started expanding my Poland collection about 8 years ago, WCN, one of the largest Polish auction houses were at 6%. And shipping by registered mail was at $6. They've since moved up, but I think are still under 20% They also have a lot of other European material, especially German and Low Countries.