While it is common, and even expected, to negotiate prices for homes or cars, most of those in the Western world would never dream of doing so in a store or with a vendor. The price is marked on a price tag, so that is what we pay. It would be rude to haggle, not to mention futile. In Thailand, as in most of Asia, bartering is the norm, and in fact, it is rude not to barter. For those unfamiliar with this tradition, how do you know when to barter and when to pay the asking price? How do you ensure you are paying the proper price that is fair to both you and the vendor?
Just as you can be thought rude or uncouth for failing to barter with vendors, so too can you be thought arrogant or cheap if you barter at the wrong time. Many in the Middle East and, to a lesser extent, Asia believe that there is nothing on Earth for which you cannot barter. In terms of cultural faux pas, though, you want to stay away from bartering in department stores, malls, grocery stores, or for scheduled buses or ferries. If you are dining at a restaurant by yourself or with a small party, you will not want to barter.
There are a few exceptions, however. If you are eating with a large party, you may negotiate the rates before you eat. If you do it after, you will be looked upon as very cheap or unknowledgeable. You may sometimes barter the price for high ticket items in a department store, such as jewelry, or when you are buying an item in bulk. You may also offer to pay cash for a discount. Some stores will take off five to ten percent if you use cash instead of a credit card, but this is far from universal.
Before you hit the streets of Thailand, brush up on your bartering skills. While there are some intricacies you should know, in general, you want to be very pleasant. Never raise your voice, and treat bartering like a game. It can be intimidating for the uninitiated, but it helps to know that this is largely meant to be an enjoyable experience for vendor and buyer. Start in Thai, saying, "Sawadee krap/ka, nee tao rai na krap/ka?" or Hello. How much is this?
Don't take it too seriously, play along, and above all, always pay a fair price for goods. Vendors will often take off ten to twenty-five percent of their asking price through the bargaining process; unless it is a very expensive item, don't haggle too much more than that. Remember that as a tourist, you have considerably more money than the vendor.