Our approach was easy once we decided on the TT we wanted. Our budget said a used TT and between the area dealers we winnowed it down to four units. Of the four we settled on the one closest to our “prefect” trailer.
I looked up the Nada used trailer value and offered it to the dealer as the final price, including taxes, prep charges, hitch and any other fees he might have etc. It was the number I was going to write on the check. The dealer agreed.
All was not done yet because the dealer was satisfied but the State wanted their license fees, the insurance company needed their money, and on a used unit there can be some merit to an extended insurance policy.
Because of time and place there will always be those who got a better deal and those who did worse. If it meets your needs and budget at the time, generally it is a good deal.
Do not be in a hurry and take the time to shop. Like the popular chip maker says "They'll make more". :)