I have found FB collectors pages to be good. I started one myself with something I collect and it is not only sharing information, but items for sale. All of the deep pocket collectors belong so if someone has something pretty valuable to sell; chances are they will get their asking price and not have to pay EBAY fees. I have purchased items myself from FB collector pages, FB marketplace, Mercari, ETSY....I collect some OOP vinyls and can find them on Discogs. I don't know if there is a comic site where you can sell. As a buyer, I really don't like bidding on auctions anymore and prefer the seller to just set the price they want and consider offers. For now, EBAY is still the major place, but I am definitely seeing alternative sites and ways sellers are taking their wares and getting as much if not more than they would on EBAY.
"The farther we go, the more the ultimate explanation recedes from us, and all we have left is faith."
~Vaclav Hlavaty