What to do if a model was stolen?

Contact support, they will investigate.

Report that seller to the support team

Today the user deleted my model.

If he steals your model. I think other work may not be his job either.

Some models look very similar. Real thief will not use seller's renders. So as a conclusion - it is difficult for admin to decide is model is the same or only looks like yours.

I think every creator of the model knows his model very well and the small details by which you can accurately find out your model.

Some thieves also started to make changes in the mesh in hope to pretend that the model is different, but it's very easy to prove that the model is stolen as the majority of the points will coincide perfectly when matched. I find these attempts pathetic...