Shop owners probably get a commission for having an ATM in front of their store: there are countless ATMs all over Chiang Mai. The system works pretty much the same everywhere: the fee is 220 THB, no matter how much money you withdraw. At the end, you’ll always be asked “with conversion” or “without conversion” — always click “without,” that will save you a few euros on the exchange rate.
Thailand still mainly runs on cash, although that’s changing quickly. You can pay with your bank card at more and more places, and contactless payments like Google Pay and Apple Pay are increasingly accepted on card terminals.
Also check out services like Wise and Revolut, where you can top up a balance and withdraw cash up to a certain limit without fees. Another advantage is that if you lose your bank card, you can easily order a replacement virtual card to use with Google Pay or Apple Pay.
If you want to bring euros to Thailand, that’s possible — you can exchange them fairly easily at offices like Super Rich, usually at a good rate. In Chiang Mai, there’s a branch right opposite Zoe in Yellow.