Browsing makerworld, etsy and others, I see things like Mickey Mouse STL file for sale on etsy for 2 bucks. This isn’t sold by disney, just a person created a model of mickey for sale, is that legal? Can I sell a drawing of a character I didn’t create? Can I sell a model of a NFL or NHL player? Can I sell a model of a Ferrari?
User-content market sites allow you to do anything you want. Literally. It won’t stop you.
If Disney, Nintendo, $insert_rightsholder_here sees it, one of the things they are allowed to do is request to have your items taken down. After that, one of the things they are allowed to do is pursue legal action in court that will compel the user-content market to disclose the revenue you received from the items. Then another fun thing they can do is to sue you for that amount, plus legal fees, plus punitive amounts.
Depending on the country/jurisdiction you live in, some of those things won’t apply.
If you didn’t design it and it isn’t clearly in the public domain, assume you need a licence. Etsy is full of unlicensed fan models, but “everyone else does it” won’t stop a takedown, a DMCA notice, or even a lawsuit once the right-holder notices.