Want to buy a bicycle in Las Terrenas

My advice is to bring your bike with you when you arrive here.  We bought new bikes in Canada.  We made sure to ask the store for the boxes they came in.  We used them for the summer to make sure everything was good, and then took the seat, pedals and front wheel off, loosened the handlebar so it twisted sideways, and stuffed them back in the box for the flight to the DR.  Most important is to let some air out of the tires so they don't explode during the flight.  We bought quality bikes, locks and saddlebags, along with helmets and lights before arriving.  I would also add at least one mirror and an electric horn.  Nobody understands what a bicycle bell means when they hear it, but the electric horn gets attention.  The other bonus is the bike boxes have a higher weight limit, so you can throw in the tire pump, tools, or anything else heavy that you don't want in your suitcase.  Be aware customs on departure will open the boxes and swab for drugs/explosives before they go through the Xray machine.  Our bikes saw solid use as transport and grocery-getters for a while before we ended up getting a vehicle.