You're not just selling a neutral tool here, you're actually printing the potentially infringing art.
> Also there is no way knowing whether I sold any mickey mouse shirts.
Think this statement through. I can come up with a couple of ways for a rights-holder to figure out if you're selling merchandise that infringes on their marks. They can attempt to order one themselves. They can see a tweet where someone shares the cool t-shirt they bought from you.
You're probably not actually in much danger here, but I would still take the hazard seriously if I were you. Be careful.
Currently, I review all created designs before printing, so that would be a way of not infringing, I. E. Cancel orders which are potentially infringing
https://www.npr.org/2022/09/13/1122820376/the-good-the-bad-a...