Yes, you have to pay for the plot at full price after it's relinquished and as far as specifics I think someone else pointed out in another thread how the GMs might see it as against TOS, but I don't think there's anything specific that says not to sell them. People have been getting warnings and such from GMs over it though and it seems to be a grey area that each GM sees differently. Not worth buying considering the upcoming patch is decreasing prices and greatly increasing the housing available (as well as the possible issues if the sale is reported).