What is the local Thai brokerage commission?

It's 0.25% of the Baht amount of stock bought or sold, or a total of 0.5% for the round trip on a buy/sell transaction.  (Plus the 7% VAT tax on that commission).  Sometimes there is a minimum commission on smallest orders.  If you trade on-line with a Thai broker (which I advocate) the transaction commission can be as low as 0.15%.  Beware that Thai stocks bought/sold outside of Thailand often have much higher broker transactions costs. (Commissions). There is currently some talk about a small transaction tax on Thai stocks, but it would be minimum and not much if at all affect smaller investors. Stay tuned.  (January 2 2022).