Outside of shops with marked prices, haggling is the norm in most Southeast Asian countries. Remember that it is an art, not a battle of wills, and the trick is to find a price that makes everyone happy. Avoid letting anger or frustration enter into the bargaining process. Typically, the vendor starts high, the buyer starts low, and eventually you'll reach a price that adds up for both parties.
The Art of Haggling
Haggling is a way of life in Southeast Asia, but for newcomers to the game, here are the ground rules. Step one is to ask the price and then counter with a lower offer. Suggesting half the asked price is a reasonable starting point, but expect to go higher to reach a final agreed price. After a few offers and counter-offers, you should reach a price that works for everyone. If not, politely say the price is too high and walk away; another vendor may accept your price, or you may be trying to get something for less than the going rate.
Most importantly, haggling should be a good-natured rather than angry process. Being aggressive or rude while haggling will cause everyone present to lose face, something highly frowned upon in Southeast Asia. Don't start to haggle unless you're serious about buying. If you become angry or visibly frustrated, you've lost the game. At the end of the dance, you may end up paying a little more than a local would pay, but the difference is unlikely to make a serious dent in your wallet.
It is also customary (and mandatory) to bargain for chartered transport. Tourists are often taken advantage of by drivers so ask at your guesthouse how much a trip should cost before chartering a vehicle. Expect a bit of back and forth before you agree on a price. If the driver won't budge, then politely decline the service and move on.