A filter as you described would not worry me, but I have never paid so much for an air filter that I could save $10 after the shipping fee that a small time seller on ebay would be adding on to final price, unless it was some global ebay dolllars-off coupon promo.
Contamination? Not at all, if it's just dust from sitting that will blow off fine. The only NOS issue I'd have is if it has an integral rubber/foam surround to seal and it's so extremely old that it has lost all pliability and crumbles or is hard as a rock so it doesn't make a seal. That usually takes 20 odd years or a very bad, chemically polluted storage environment (or stored out in the open exposed to direct sunlight).
You never know though, there are some jokers out there that will sell something they found used in a dumpster so above all I'd look at their feedback rating.