Now Playing: Psycroptic
You get your amateurs and your professionals in any business. It starts with the schoolyard comic swap and winds up in a comic warehouse. Pretty soon your hobby has become an expensive or lucrative (depending on which side of the counter you happen to be) pastime and you're there with your reserve price for that near mint edition Exciting Comics #1 .
If you want to remain anonymous or small time then just offload a few of your doubles on eBay or, if you fancy competing against an established, if niche, market then you're better to specialise. King's Comics and Comic Kingdom leave no room for jesters on Sydney real estate, The Land Beyond Beyond being long gone and the Phantom Zone further west.
Who says you need a shop though? You can operate from home by mail order or, assuming you're not a luddite, put up a webpage. You can sell random 'finds' after you've read them, through an ad in the local paper, or via a free online classified. If you're feeling generous, you can leave the occasional crumpled comic in the backpacker's hostel [card with web address discreetly stapled to the inside back cover optional].
If there are comics you just want to get rid of, sell them at jumble sale or fete.
If you want to sell the art of Gary Frank or the stories of Peter David, you need to have an organised supply. Their output must still be available at a competitive price as they are working artists but constructing a sales showcase around their work is another matter.