Personally, I wouldn't touch 'em.
First, they are most likely inappropriately acquired from the military; do you think they just give plates away or you keep 'em when you get out? While I've seen some loose accounting for plates when we went from IIIs to IVs, they are still accountable items.
So while it may be a good deal, would you knowingly buy stolen property? Just sayin'...
Second, there are non-stolen plates available from commercial retailers, of which you can be certain of the quality, rating and condition.