are there rules for the market such as a minimun percant off? for example if i sold something for 1 TC that was usually 50000TC would i get banned?

No, it's allowed aslong as you didn't receive that item illegally, though selling something so cheap might get some people suspicious.

Well, honestly, who cares of how much you sell an item ?

As long as you didn't steal it, you can do whatever you want of it.

Even sell it for 0 tc.