I can share one thing, check the trailer CAREFULLY.
The rolled steel trailers rust, so you must crawl under the trailer and check the underside of all members for rust and cracking. The weight of the boat on top of a rusted cross member will start to crack the bottom of the cross member. When that happens you just bought yourself a new 4500 dollar trailer. Ask me how I know
I have found this website, BBC, and craigslist to be some of the best resources to find boats for sale... but you now get to play the "photo
When I was buying my boat, I found out quickly that a lot of folks photos (especially on craigslist) were... hmm creative... I found some were taken the day they bought the boat, I drive five hours to find a hulk of junk on a trailer with flat tires and covered in leaves. Oh my gosh, I gave one of them a serious piece of my mind over it.
SO ASK on the phone, "when were these photos taken?"
Let me ask you this too, have you got money burning a hole in your pocket and you want something recent? Or are you going for the "lighter on the pockets" model? I chose the later, even though I could have gone out and bought a brand new boat, I decided to go the 12k route - and there are some EXCELLENT boats that get ignored a lot out there in that price range... like the pro-crafts, and the Allison's, and the earlier pantera II's, and the champions, and the stratos, and the Astro's, and the Cobras.