6K sounds a bit high for a trailer that old. Even in my overpriced area, 6K would get you a 2005ish model. Also, the ad says the tires were new in 2006 which means they were due to be replaced in 2011. My understanding is tires rot out after 5 years whether used or not. That might be extended since this trailer was stored inside, but I would take a good look at those tires for dry rot.
I haven't heard anything bad about that brand either.