So..... a buyer for your tractor travels a X (many?) number of miles to purchase your tractor. Unbeknownst to him it has an unpaid lien.
You collect the thousands of dollars cash, and stuff it in your pocket.
You give the buyer a hand written receipt.
The buyer drives away with your (now his) tractor on his trailer.
The buyer is completely safe! How would ANY lien holder ever locate that tractor to repossess?
Search all 50 states for every used tractor out there?
Check all used tractors shipped out of US ports?
That tractor is GONE!
The issue is now a legal one, between the lien holder and the seller.
As the buyer, with a receipt from the seller, you are not ever even aware that there was a lien issue.