Where can a friend go to find a good used Travel Trailer?

THere is no one place a person can go to get a good used TT. No matter who you buy from, you have to do your own do diligence and even then, you're taking a chance.
It might cost more but if you go to a long term dealer with good reviews you probably have the best chances.
Private sales, no matter how cute and cuddly they seem to be, can be a real gamble.