It has been mentioned before that selling houses is a violation of the terms and conditions. I'm not sure where in the t/c it says so though, but there was a recent forum post about it. I think it's due to the whole buy a place, then sell it for gil, then the person has to pay more gil to buy the plot, then more for the housing permit, thus encouraging RMT activity. I think it'll ease up if they fix the housing issue.