I am regularly at PoP airport &see the baggage handlers trying to "JUMP" on an unsuspecting tourist to book their place in taking the bags some 50 or 60 yards to the bus. Yes, they 'demand' US $5 or US $10, sometimes more. IF you accept their help, pay them only what YOU consider is fair but always explain why with a smile!!
As Jim says - Say NO (again, with a smile) & continue to be firm if they try to force themselves on you. If they persist, call one of the policemen across to move the handler away or find one of the hardpressed tour company reps to assist you get rid of the guy. Generally this is not necessary.
Have a great time at Coconut Palms, it is a very tranquil place but DO get down to Cabarete, especially for the night life on the beach. - Grahame.