Brokers
Are you bringing the goods by sea or air?
In the past you could pay a broker to get you the best rates but now its difficult. What a broker can do for you these days is clear the goods quickly. Some brokers are more expensive than others but they all do basically the same thing. Most goods are valued on the amount on the original invoice that is sent with the merchandise. They include the the cost of shipping in the whole value.
Besides the duties imposed that differ depending what it is there is an exchange commision that can put the duties upto 100%. I know of a company that regularly does broker services thru las Americas Santo Domingo, if you are interested.