Whilst we may be able to troubleshoot, General Discussion is not the place to do so.
As above I would advice that you speak with the server owners first and determine the behaviour is not in fact a feature of that particular server.
This is the correct way to do it. You can also assign a sellPrice like the example above to save you from having to double the price (because all buy prices are halved when selling back unless you have a sellPrice set).
It is the year 2039. After the resource depleting conflict in Greece, Europe suffers from a new deflation crisis, leading the crime rate to a new peak in history. Members of the North Atlantic Treaty Organization Security Council are forced to react. Being a desperate alternative to overcrowded and prohibitive prisons, offenders are now being sent to EXILE.