It is a secondhand market. Items like jewelries, antiques, watches and others precious things can all be traded there. You can ask the shopkeeper to keep the item for you if you would like to buy it back in future. On the other hand, pawnshop has another function of being a souvenir store. The items there are on sale, and you can buy whatever you like at a fair price.. However, you should make sure that you can recognize the difference between the genuine article and the fake one before you make the deal.
You can find pawnshops are quite ubiquitous in Macau, especially around the area of casinos (like Lisboa Casino), because the gamblers will sell their belongings for money as their bet.