Strange people buying my models

It sounds suspicious. I'm not sure what you should do though, unless you find evidence that the customer is not respecting the license. Hopefully there won't be a CC charge back.

I would suggest to contact the support, they should be able to investigate the case and tell you if there is something to worry about. Sometimes on cgtrader you get sales from corporate clients, but from your description it doesn't look that's the case.

Update:
It was a fraudulent user after all, I am safe tho.
The sad thing is that in the end I made no money ;-;, but I will still do my best to get better and maybe get more sales xD