Ye I understand you,i suggest that a player can buy / sell a zone only some specific times.For example if he bought a zone once then sold it then bought it again and going to sell it he won't be able to do it.That was just an example.
No. The idea of sell it is to get the same amount. I bet you don't have a zone, so imagine you do: would you like to lose 1m by selling your 10m zone? I bet you won't, who would like to lose money while trying to get it?