One market really worth visiting in Halong is the one in Bai Chay that is open in the nights as well. It has kiosks full of interesting knick knacks sold at reasonable prices. Vietnam is known for its lacquer ware of which you find a good variety here, along with a variety of chopsticks.

You can also keep an eye out for charming trinkets and art objects. Do remember to bargain though. It makes sense to offer half of what the shopkeepers quote initially. If they do not agree use the age-old trick of walking ahead to some other kiosk. Chances are the shopkeeper will call you back offering the price you suggested!