I think Namejet tries to approve private sellers that showcase domains in their application that would be of interest to their buyers.
Back when I got approved it took a couple of tries. Once I realized the type of domains that were selling on NJ, I applied with a list of similar domains. Then approval came right away.
Once approved, private sellers can list pretty much anything. Just have to get through the approval process. Also doesn't hurt to pick up the phone and call. I did in the beginning just to meet a few key employees. Have built pretty good relationships since then.
Hope this helps.