Finally someone has had the guts to tell it like it is. Yes, there are a number of greedy tube sellers on this site that are less than scrupulous, yet have "perfect" feedback because foolish audiophiles believe the lies and misrepresentations. These same audiophiles don't know the difference, and are blissfully ignorant that they have purchased used, poorly matched, and mediocre-sounding tubes.
These same sellers go to hamfests and flea markets, picking up old, used tubes, and then pawning them off as NOS or near NOS on the innocent.
Beware of just following feedback on these tube sellers for these very reasons.
Jim McShane and Kevin Deal have very good reputations, as does Andy Bowman @ Vintage Tube Services. Some of the prices are unjustifiable, in my mind, but silly audiophiles have driven this madness this far, simply by being willing to pay these exorbitant prices.
NOS = New. A new tube will look new, 90% of the time. If you know how to look at it, you can tell JUST from that. The lettering, the base, the pins, the flashing.
I also have been told that tubes with many hours on them can measure "NOS", but their life is past the 50% mark. Eventually, a decline in the reading will plummet.