I think the merchant needs a book on Stranger Danger.
Srsly, a guy in a large trench coat, with a lot of pockets, who lurks in dark places and will say "ahh..i'll buy it at a high price" to a bunch of different coloured leaves mixed together.
He Belongs in GTA:IV or something...
10 - Supply Depot (1)
13 - Barracks
15 - Marine (1)
16 - Orbital Command + Supply Depot (2)
16 @100% Marine (1) - Command Center (2)
21 - Bunker (1) + Barracks (2) (3)