There is no mandatory requirement to tip anyone, but small gratuities for excellent service are very much appreciated. Therefore, there is a general acceptation for getting a tip whenever you are satisfied while having a massage, eating in the restaurant, using a taxi, or having a tour with a licensed tour guide. Although it is way more polite to tip with the notes (20, 50, 100, 500 and 1000) that with the coins.
You are not expected to leave a tip when you eat street food, but anyway it is nice to do so when the food is good. A 10-20THB tip is nothing that might change your travel budget but can make a big difference for the people servicing you.
At markets and souvenir shops, the prices are often inflated, partly because of the knowledge that tourists will want to try and reduce the amount. Haggling is generally expected in the absence of market prices. Although before you start bargaining, make up your mind on what you think is a fair price for the item of interest. If you don’t know the price level, have a look around and ask a few different shops about their rates on similar themes. You will quickly find out whether you can agree on a price. Mind out that is nasty form to go through the motions of haggling if you are not interested in making a deal at any cost. Likewise, if the seller agrees to your price, it is not cool to say you do not want the item or service.
Transportation, souvenirs, massages, etc. are the easiest to bargain. Especially when you are trying to make a deal for a group of a few of you or buying a few items from one seller. If you want to make it friendlier, it might be a good idea to teach yourself how to correctly say hello in Thai (Sawadee Kha/Khrap). Moreover, keep it in your mind that you are dealing with the prices in Thailand – The Land of Smile! Keep smiling than not only while haggling, but as often as possible. That is the easiest and international way to start the conversation with anybody around you.