For buying baht, US dollars are the most readily acceptable currency, though travellers' cheques get a better rate than cash. Credit cards are becoming increasingly acceptable in quality shops, hotels and restaurants. Visa is the most useful, followed by MasterCard. ATMs which accept Visa and other credit cards are easily found in the larger cities, and many exchange booths will give you a cash advance on your credit card. Tipping is not customary in Thailand, although Thais are getting used to the idea in upmarket hotels.
Bargaining is common practice in markets and tourist shops, and when catching non-metered taxis.
Treat it as a form of social discourse rather than a matter of life and death.