I always give the same advice when it comes to child trailers- Buy a "name brand" used trailer. I have used a bunch of different trailers and have bought all of them from Craigslist or Play it Again. You should look for brands like Burley, Chariot, Trek, Co Pilot, etc. There are a few Schwinn ones that are higher end quality too, but you have to figure out which models are the good ones. I have never paid more than $120 for any of the "high end" trailers.
Bruce