I sell physical goods like comics and pins through etsy and I do sell downloadable pdf versions of my comic on gumroad with a pay what you want model, seeing as people can already read my comic for free here, I treat it like a tip jar.
There's redbubble too which is great if you don't want to shell out for printing costs and such up front, but you're not going to see massive profits unless you sell a lot, and as bad as it sounds... fan art seems to be what sells there (though they seem been cracking down on that sort of thing). I had a friend that drew some gorgeous work (which I have a few prints of) but there was a particular mashup that sold ridiculously well and ended up getting stolen and resold by some company on Amazon.