Sure wish that we had enough information to be helpful....
You seem to be a bit shy. Don't be intimidated by asking the seller to completely display the trailer for you. They should be willing and happy to show you that everything works and how it works. If something doesn't work, the seller should be open about it and allow you to evaluate the cost of repair or replacement of that item.
A seller should be happy to let you take pics, ask questions and display the pics to others to ask questions. If the seller doesn't like any of these things, there's a good chance that they are trying to hide something.
If this guy thinks that the trailer is worth $6K, he should be willing to let you take pics and ask opinions of current TM owners to reassure you that the seller is right.