Can i sell old cable boxes?

I have a bunch of old cable boxes thats atleast 5 years old or more, 2 of them belong to charter and some direct tv and Hughes. I dont know any history on any of them, like if the bill was never paid and the box never got returned or what. I want to sell them cause I have Dish Network and i dont think i can use any of them. Is it illegal to do this or could i get in trouble for even having them?