Uhm Got to src>Config.txt
And search for
ADMIN_CAN_TRADE
you see this then
public static final boolean ADMIN_CAN_TRADE = true; //can admins trade?
public static final boolean ADMIN_CAN_SELL_ITEMS = true; // can admins sell items?
public static final boolean ADMIN_DROP_ITEMS = true; // can admin drop items?
Change it 2 false