Well, I'll add my $.02 for what its worth. I am certainly no expert but I have looked at a lot of Daysailers on Craig's and in person.
In the order of the links in your post I would go see #1, #3 and #4. It is hard to ascertain the details or the soundness of the vessel from photos. But, every picture tells a story and when I see the stays and halyards haphazardly strewn about the boat and other junk just laying in the cockpit I feel that it says something about how the owner cared for it. Not always, but it generally will make me pass unless its a really sweet deal.
In ads 1, 3 and 4 you see a boat that the owner/seller at least cared enough to show it in its best state.
#1 looks like its in the best shape of the 3 in the photo. #3 is also nice (and the same color/style as mine so I'm biased) but if its a 1973 which I suspect it is its actually more like 43 years old, not the 30 the seller is claiming and although it comes with a nice canvas sail/boom cover, that could mean that the boat spent a lot of time in the water on a dock slip or mooring. Finally, #4 seems solid and the new standing rigging is a plus. Go take a look and offer the sellers a few hundred less than they're asking and see what happens.
I'm sure some of the other regulars will chime in with their experience. There's some really good posts on this board about what to look for when you go see it. Just use the search tool or my personal favorite is to preface a query in Google's search engine like this:
forum.daysailer.org what to look forhttps://www.google.com/webhp?sourceid=c ... look%20forAnyhow, have fun and best of luck to you in your quest. You'll find a good one. Your in a buyer's market out there with lots to chose from.
Eric