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?
Dont 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, dont haggle too much more than that. Remember that as a tourist, you have considerably more money than the vendor.
Source: By: Enid Glasgow