Update: Luggage handling fees only apply to cabs heading to and from Bangkok airports: Land Transport Dept
Under the new regulations, taxis will be allowed to charge luggage handling fees as follows:
• Bt20 for every bag that exceed 26 inches in width, height or length.
• Bt20 for every additional item of luggage after the first two.
• No more than Bt100 per piece for sports equipment like golf bags, bicycles, surfboards or musical instruments that are 50 inches or more in size.
• No more than Bt100 for equipment, tools or appliances that are 50 inches or more in size.
The cabbie is required to inform the passenger in advance about the extra handling fees.
No charges will be allowed for carry-on baggage such as handbag, computer bag, backpack or personal belongings carried by the passenger.