Gumroad appears, and granted this is after reading about it for about five minutes, to be a sort of eBay/Etsy sort of place where people can sell their own stuff direct. I'm sure those analogies are not precise.
https://en.wikipedia.org/wiki/GumroadIt's a legit company as far as I can tell, but it's basically like eBay, just kind of a channel or broker between the buyer and the seller.
I do think the whole website and presentation is almost *too* barebones. No mention of who is the actual publisher/seller, and I usually get a bit nervous when I click to buy and I get a one-screen pop up that, when filled out, immediately *completes* the transaction. No interstitial pages where you can confirm your order prior to completing it, etc.