Cyclonicman, you have been very fortunate. I would say most of those that I've dealt with on AudiogoN have integrity, but not all. As Bill notes following your post, everyone selling a used phono cartridge has only used it for a few LP's. ;D
I'm aware that an odometer can be tampered with, but it is an illegal offense. There's nothing illegal about mis-guessing the hours on used tubes, phono cartridges, etc.
One can only hope to deal with someone of integrity. Most have great intentions, but their actual memory may be a bit foggy. I'm not insinuating that their is actual fraud, though I have been involved in one deal where this was the case. I just think that many 'guess' at the hour rating, and do so in a way that will help their sale.
Cheers,
John