If this unit is upgraded to V4 then Meridian America will tell you straight away. They also put a large upgrade sticker on the side of the box so that would say also. I think the seller is confused. I bet he has been told that Meridian have updated the software when it was there and he is putting 2 & 2 together and coming back with V4.
My bet is it's a version 2 with the newest software, whatever that may be.