The real estate agents in the Pattaya region usually ask for between 3% and 5% commission of the selling price, which is typically paid for by the seller. Subsequently, the agent’s commission is included in the advertised price of the property.
Note: this is negotiable.
As well as the agent's commission there is a transfer fee of 2% of the purchase price to be paid to the Thailand Land Department.
The transfer fee is usually paid by the buyer, but many negotiate to pay 50/50 between the buyer and the seller.
There is also a 0.5% stamp duty to be paid, usually paid by the seller, but many also negotiate to pay 50/50 between the buyer and the seller.