"Unit Trading" turns "Unit Trading" on or off on multiplayer maps. You need to set up your units for each team the correct way (see any of the basic mapmaking guides) so you will have 'extra' units to trade.
'Reverb Properties' effects the quality of sounds in game. The settings change how long and loud sounds like explosions will 'echo'. I don't know if they work or not, I can't recall ever changing them.