@GeorgiaB hi, there are no extra charges to use the card in-store. You are limited to 6000 EUR/month due to exchange limits (more than that occurs a charge).
Many shops in Thailand will ask you to charge your card in YOUR currency ( EUR or GBP or whatever). Just answer no, charge me in local currency (THB in this case) and you will avoid a 3% or possibly more surcharge. Just let the Revolut do the conversion.
Weekends are a whole different story, because Revolut charges a % due to closed currency markets, meaning that you pay more than necessary.
Either avoid using a card during weekends, or purchase THB within the app in advance to secure a good rate during the week, or use a different card during the week.
ATMs in thailand all charge withdrawal fee now, so there is no way to avoid that. Searching for a free ATM is pointless now. (last free ATM - Citibank in BKK started charging ATM fee in August, 2016). You can however use ATMs that allow withdrawal of 30.000 THB instead of common 20.000 as you will still be charged the exact same fee.