I, personally, don't think it has anything to do with the Second Amendment or the current Federal administration. I just think that good guns have always sold for a premium, not talking here of surplus or police trade ins, but good guns. And auctions, well anytime you're competing at auction you'll be up against that ONE GUY, that "just gotta has" that gun to complete his collection. He and his ilk constantly drive gun prices higher.
Add in the fact that all items offered for sale will have exposure to a much larger group of potential buyers than the same item would have in a local gun store or smaller gun show.
Keep in mind, too, that gun auction sites force a premium over fair market value, the dealer and the site need to make their money as well, and add in another little bit of cash for the shipping and FFL transfer.
In a more prosperous economy, with more disposable income, gun prices might trend even higher.