I favor buying from private sellers, even better if they're local. Best is to buy from someone in a local military vehicle club or someone here because those sellers have reputations to maintain. Also know what you're getting into - engage the seller, talk about the truck, take it for a test drive.
I remember reading a thread here awhile back about someone who spent around $30k on a 5-ton wrecker that was gone through buy one of the popular truck surplus dealers. The buyer had nothing but problems from delivery on. While it's my understanding that the dealer solved the problems, it shows that just because you buy from a surplus truck dealer doesn't guarantee that something will break shortly after the truck rolls off the trailer.
That said, I take comfort in knowing that I may have the same problems buying from a private seller but for 1/3 the price or less of surplus truck dealers
Truck parts though? The dealers are mostly where it's at, though I peruse the classifieds here sometimes!
I just looked at the location of each poster here so far and everyone's from a different state. Isn't this place great?