Why are exchange rates different at different banks

In order to make a profit , banks and other money changers use different rates for buying and selling currency. The online rates you see are probably mid-rates - half-way between the buying and selling rates. Of course, just to be on the safe side, banks also charge commission on the transaction...

Why is it that, when I check exchange rates ... - The Guardian

 

 

For my charts I use BOT Bank of Thailand 

สกลนคร Sakon Nakhon