First of all, I don't think there is that much new construction going on. Some of the construction maybe projects that where not completed do to poor financing; planning and other problems. Most of these are not actively under construction but maybe completed someday.
Real estate did not take the beating that it took in the USA down here. Some units are bought by people who will rent them out and hope to retire here in the future. I haven't heard of too many buying to flip units but I suppose it happens.
There are many good condos here that are reasonably priced that will fulfill their obligations to the owners and be pleasant places to live. If you are worried about preconstruction projects or half constructed projects why don't you purchase a completed or nearly completed project?
Please note that I have nothing to do with the real estate market here and I'm not an expert. I do own a condo here and have for over 5 years. I think I have a good understanding of the finances and workings of that particular place in paradise and I'm happy with my purchase.
Do what I did, come down on vacation look around and talk to people. After several visits find a real estate agent who has been around awhile and has a good reputation. Then and only then make your decision. To come down here, spend a few days and make a decision like that does not make sense to me. Good luck.
Somewhere on a beach in Belize