What is your idea of "high end"? I've sold mid-range stuff on this site ($500-1000 handguns) but expensive guns tend to sit until people drop prices lower than I feel I'd pay in consignment fees. So I tend to take more expensive items straight to consignment. I forget the exact prices, but I had a few items here for ~$1200. I dropped the price a couple times and they still didn't sell. Took them to consignment at $1300 and they sold in a day.
I've bought a few things on Gunbroker over the years but never sold anything there. I'd probably make more money on the sales but I don't sell that often (just when cleaning out items that haven't left the safe in a decade) so I've only sold locally.
I'm surprised there isn't a shop that caters to the "sell it for me" market. If someone gave a fair price like 10% non-refundable listing fee plus some % of profit above your target price, I'd use that service. I've done that with a neighbor for non-guns on FB Marketplace. I don't have time to deal with tire kickers and my neighbor loves that stuff. So I'll give him a thing and say "I just want $200 for it - anything more you can keep", and we're both happy.