If I knew a box had a lien on it, I'd stay away, but I really think an outside buyer shouldn't have to hire a private investigator if they're buying a used tool box. It's between the tool company and the borrower to remedy a situation when the original buyer can't pay off the remaining debt.
You make it sound like it's some huge hassle to find out if a box has a lein. It took me one 5 min phone call to Matco's credit department, and they were more than happy to run the serial number. Cost me nothing, and I was talking about a box that I would have offered to pay more than $5k.
I agree that this whole situation ***** for an unsuspecting buyer, but as they say, ignorance of the law is no excuse. What is a good thing, is that fellow GJ members will hopefully take heed, and not be burned. And perhaps prevent some others from similar fate by sharing this info with friends who are shopping for used toolboxes.