There is a small flea market where you can buy souvenirs and handcrafts. The people will seem friendly but depending on your looks they'll try to charge up to 10 times the price of each article.
Remember to bargain as much as possible if you're determined on buying but most things can be found quite cheaper in Santo Domingo or any other town.
Unique Suggestions: Some people will even offer you taking the piece with you and pay the next day. It will be up to you if you go back to pay or just take the souvenir for free.
Some others will even give away a small gift to you while bargaining for a larger one, whose price is inflated. If this is the case I'll suggest to take the gift and buy the other piece somewhere else.
If you go to Saona or Piscina Natural be sure to compare prices. Often you can get quite good deals if you stay away from the resort crowd and book a trip at one of the smaller diving schools outside the resorts.