Currency Exchange is always a tricky business as it varies not only from country to country by even from one part of a city to another. Luckily for visitors to Bangkok in Thailand exchange rates are very good from most foreign countries and no commission is common and rates hold pretty standard at various venues.
Often airports are terrible places to exchange currency due to commissions and bad rates. At Bangkok’s main international airport Suvarnabhumi one can exchange inside any time of day or night with no commission, the kiosks there are run directly by the banks. Rates may be just a tenth of a cent higher than what one will find in town.
In Bangkok itself there are plenty of exchange booths in public areas, in shopping malls and at any bank. Just a note that almost all banks close at 3:30pm so be sure and head early if going to the bank. Almost every kiosk and bank we’ve experienced gave a fair rate and the kinds of change requested, but to do a simple calculation before handing the money to be exchanged will not hurt anyone and it is the way to be sure one is receiving a fair exchange. Many hotels will also exchange currency but these are the most likely to charge a commission. Credit cards work almost everywhere in Bangkok, but its good to have cash and coins in hand for public transit, marketplace bargaining and food stall purchases. ATM Machines are widely available in the city and getting cash from these machines using a debit card may be a good idea and a way to always receive a very fair exchange, just remember that there is always a little commission charged by the local bank to these kind of transactions.