As a general rule, to successfully flip houses you need to bring together a few factors:
1) A rising housing market
2) A property that is undervalued, or one to which you can add a disproportionate value with capital infusion
3) A quick enough sale so that the interest on the mortgage (or the opportunity cost on the money spent if you're doing it out of pocket) doesn't eat up your profits
All this presupposes you'll cover the agency costs, attorney fees and taxes with the increased sale price when you sell it and still have room for a tidy profit.
Obviously, experience in construction/renovation or at least good relations with someone who does is an invaluable asset.
I think it's fair to say that the housing market, at least in Cabarete and Sosua in on a continuing upswing.
There are a lot of owners who want to get rid of their houses, so there are some great deals out there. Whether or not what they consider a reasonable selling price is actually below market value is something you have to look at on a case by case basis. Some people are desperate to sell and will give you a 'steal' price. Others are nuts and massively overvalue their homes.
The sticking point comes when you want to sell the house. As has been pointed out, there is a lot of inventory sitting around for years doing nothing. Over time, this dormancy will eat away whatever profit you might have made. Of course, people are buying houses and condo's like it's going out of style, so if you market and price it properly and it's an attractive property in an attractive neighbourhood, there's no reason why you can't turn a profit in a reasonable amount of time.
Understand this, however: in New York, or Montreal, or Berlin or anywhere like that, if you need to dump a property for whatever reason, you need merely underprice it and someone will pick it up relatively quickly. Not the case in the DR. You get stuck with a property, you can be stuck for a long time.
Fair enough?