An uncle died and left me a large quantity of Super X .38 wadcutter premium target ammo from the 1960s. He'd always stored it properly. It's still the most consistent factory ammo of its type that I've ever shot and over the years I've tested every newly-made premium load I can find on paper and over the chrono. The only other .38 wadcutter target ammo that has been about as consistent (though at much lower muzzle velocity) was CCI Blazer aluminum .38 wadcutters; that stuff surprised the hell out of me and I'm sorry I didn't stock up on that lot of ammo when I first encountered it.I mirror Ben in that some of my oldest ammo was also the best stored and thus most trusted for reliability.
Point? Storage conditions are the single most important thing I want to know when someone wants to sell me old ammo.