Not on the buyers end, provided the equipment isnt illegal to possess (rifles, machine guns, sensitive equipment such as scopes, laser rangefinders, etc). From a soldier's point of view, again, speaking from experience, you can sometimes sell gear for more than it cost you to write it off-it largely depends on the equipment, and the shape it is in. There arent any legal ramifications for someone purchasing it, barring the exceptions I stated above.
Soldiers, especially good ones, are resourceful. We usually trade with other militaries for gear when we deploy, and often come up short when it comes time to turn it in. But, I couldnt purchase a british Goretex jacket for less than a few hundred $$$-but I can trade mine, and be charged $67 for my loss. Seems like a win-win to me!