The OP of the tumblr post calling out wallpart.com has made an update regarding the site. It's an information scam site. Apparently you cannot actually buy the item. They ask for your information and that's about it. Here's a screenshot I took after putting in fake information:
As you can see, they stop it there. There's no option to move on to purchase.
Here's OP's revised post.
So basically there is no profiting from our art beyond obtaining people's information (home address) which, in itself, can be used by being sold to companies for various reasons.
I urge everyone to report this website to google via https://www.google.com/safebrowsing/report_phish/