there are several very good auctioneers, never heard of Horst before but looking over upcoming sale and previous sales looks like the real deal and fees not as high as others.
I think one of the biggest is rock island auction, a no nonsense auction house. everything they do is first class, from picking up collections at your door to exceptional packing and shipping. and the grading and photos they take are some of the best out there. most every city has gun shops that will buy and some do consignment and many local auction houses are bringing in top dollar on guns recently.
its a matter of how much work you want to do. anyone can post on gun broker but then you have to pack and ship and deal with ffl stuff. for about another 10 percent these professional auctions take care of all that and send you payment when its all done.