How to politely turn down sellers in Thailand
innsent av Happy luke i Thailand forum
When going to the market, vendors will definitely try to offer you their items but if you're not interested with it you can just smile at them say "Mị̀" or just make a hand gesture that you don't want it. Thai people are friendly in nature so I don't think you'll be having a hard time regarding with this matter.
And since you're traveling to Thailand, I have a travel blog that can definitely help with to know more other spots that are worth visiting. (http://thaimtraveler.com/)