WARNING WARNING- there are many places in Sosua that rent motoconchos and scooters, but you have to be very careful when renting one. I have heard a few horror stories of unreasonable charges for very minor scratches and damage.I met a guy from New York who was charged eight hundred dollars for some scratches caused when the bike fell over.
The worst thing you can do is give your pasport for collateral.Never give up your passport for nothing to no one, not for a scooter or a car. The guy from New York did just that, and they used that against him to extort money for damage that they probably got fixed for 20 bucks.