For the double-shipping issue: Maybe the middle-man should be chosen according to the location of the Buyer. That way, the Seller sends the item to the middle-man, and when money is received, the middle-man gives the item to the Buyer at the next game the Buyer and the middle-man will attend.
I know that games during winter are not as frequent as in summer, so it would be longer to get the items.
Anyway, I don't know the exact number of transactions that occurs here on ASC, but the ratio of good transaction/a la GreenIgor transactions must tend to be in the range of 0,01%. The risk of trading on a forum, as smal as it can be, is the price you pay for the money you save on this kind of deal. Aren't able to bear the risk? Pay the full price of the retailers.