I have bought and sold TONS of items thru Craigslist while we lived in Alaska, Kansas, Oklahoma, and Maryland. If it is priced right, it sells quick.
I think the Craigslist market is best suited for average/typical items. Specialty - high end - high $ LQ trailers would probably do best advertised on Craigslist AND multiple locations with more "horse" traffic.
I do look at Horse Trailer World, mainly to get an idea of fair price for an item, and an idea of what dealerships are within a certain radius.
Ok I just sold my trailer. The buyer was from Horse trailer world and I got at least 2 possible 3 from that sight. Zero inquiries from Horse trailers galore, at least 1 from Horseclicks and at least 5 from craiglist.
Oh and the dealers would only give me 12-17K for it and I sold it for 25K to the first buyer and have several waiting if the sale falls through.
Horse Trailer World, Craigslist, and Facebook, in that order. I do usually list on Horseclicks and Horsetopia since they're free, but they're so full of spam I don't shop there, so figure others feel the same. I usually stick one up on Tack Trader too.
In the buying/selling process right now. Buyer of my trailer came from HTW. My current #1 contender for buying I found on craigslist.