like above. remember to have any form of ID with you and you will be ok. there are also 3 or 4 ATMs outside if you need cash.
I never know what card will work where, it's always a fun guessing game
you can always go to a bank and get a prepaid credit card........fees are only a few pesos and work for any supermarket or online transaction.
I just bought a refrigerator at LaSirena. We called LaSirena To see if they accepted American Express which they did next we called American Express. Everything was a go. We paid 31,975RD and 778Us came through on our card. Very easy. I think as long as you deal with reputable establishments you shouldn't have much of a problem. I'm always very careful and prefer to use cash.