Agree with Vikingstaff on the paperwork. My last boat I owned for 9 seasons. I kept every receipt, and could show/prove to the buyer that it was well maintained. So please ask for maintenance paperwork.
Not a deal breaker, but ask about the maintenance done on the trailer. When was the last time bearing were repacked or replaced. Check the electrical with your vehicle and make sure lights work. Check the tires for dry rot. There should a manufacture date on the tires. If those are the originals, and the trailer wasn't used much, the tires likely are dry rotted and need to be replaced. Like I said these things are minor, but it could give you some negotiating power.
Not a deal breaker, but ask about the maintenance done on the trailer. When was the last time bearing were repacked or replaced. Check the electrical with your vehicle and make sure lights work. Check the tires for dry rot. There should a manufacture date on the tires. If those are the originals, and the trailer wasn't used much, the tires likely are dry rotted and need to be replaced. Like I said these things are minor, but it could give you some negotiating power.