You can buy weapons, armor, consumable stuff and any other items from NPCs.Just click the Buy button behind an item like what you do in the Mall.
Find a Blackmarket Merchant in one of the main cities.
The Blackmarket Merchants will refresh their goods at 10am and 4pm each day. They only offer a limited amount of goods. The goods will be at a big discount as shown below.
The goods are divided into 3 categories: Top, Special and Cheap. Top ones will seldom be available. The Blackmarket Merchants will only offer one kind of special items each time with a 10-Voucher unit price. The Cheap goods will be at a 10% to 30% discount.