You should be honest with the fellow. I know it is hard for you to understand the concept of honesty Wes... so this is what that looks like.
That gear vendors unit was in a truck that got sent hard enough to rip the gear vendor unit out from its mounting brackets. Clean out, dragging on the ground clunking around wondering if a drive shaft broke. The drive shaft was good and kept turning fine, just the gear vendors wasnt hanging onto anything but some dirt.
It was a blast, and I laughed my head off the whole time! I had never seen an old ass diesel spin through every gear while hoping for some traction like that and it was a great time... Then when we crawled under the truck to see what was wrong I just laughed some more. And that is when we wratchet strapped it back in place and limped it back to the shop. It was a great time but this guy may like to know those details. It may, or may not, change someones mind about buying it.
It could work fine, it could just need bolted back in, but if he bought that part from you he just may end up posting in the Hall of Shame like I did after seeing your workmanship.