New tires will hide alignment and wheel bearing problems. When I was shopping used TT, I was very suspicious of any used trailers that had new tires. Even more suspicious when the salesman assured me that the owner installed new tires to give me a better value. Old, well worn tires tell the truth about the wheel condition and I'm very capable of buying new tires myself.
The same is true about painting the inside of the TT. Fresh paint can hide water and mold stains.
Honesty is the best policy - sell it as-is. If something doesn't work correctly, offer to pay a third-party dealer to fix it before the buyer makes final payment. Be sure to get a non-refundable deposit from the buyer before having it fixed so that he doesn't change his mind while the trailer is being repaired.
2015 GMC Canyon 3.6L V6 4X4 TowHaul SLE ExtCab Bronze
2016 Keystone Passport GT 2670BH
ReCurve R6 hitch, DirecLink brake controller
2005 Suzuki C50 2006 Suzuki S40