Tubes in PVS?

Certain sellers offer electron tubes that measure as being at, or near, the end of their useful life. What's your worst experience buying tubes that are about to enter a persistent vegitative state (PVS)? Did you think PVS was the name of a new tube amp? IMHO Audiogon should provide a list of tube measurements, i.e., for each type of tube, what reading qualifies it as NOS and what reading means it's near death. That would keep the sellers honest and prevent newbies from being taken advantage of.
Jay