If you have felt comfortable with the dealer you have dealt with before then go back to him.
There are good and bad in either way. We bought new from a dealer, love the trailer but will never go back to the dealer again. He was not totally honest. We would automatically think a dealer would be more honest.
I should say if I was buying used and the TT was in excellent shape, well looked after, then I would think that the owner would be very honest and show you everything you needed to know. The owner would obviously have been very proud of his toy if he looked after it.