There are two different exchange rates, onshore and the offshore rate which is around 10% lower. Confusing I know and it applies to all curriences. Exchanging money in thailand will get you the higher rate and ATM withdrawls and credit card transactions should also be at this rate. Transactions outside the country are at the lower rate and some hotel booking sites also use this lower rate.
Examples: Aus 30/26.7, UK 65/58, Euro 49/44, US&Can 33/29