You can bargain at markets or stalls on the street. A good rule of thumb is that if a shop has a solid door and windows, generally you cannot bargain there - everywhere else is fair game.
A good tip is to arrive at a market first thing in the morning. The Balinese consider the first sale of the day to be good luck, and will often make the sale for less. Ask for the “harga pagi” . Be friendly, respectful, and smile while bargaining.