I had a few incidents when the guys demanded money upfront and asked for more on transportation. On those occasions, I just told them once the services meet my expectations than I pay for the time and fun promised. The money upfront happened to those foreigners working in Thailand, two were Russians and three were from Bangaladesh. The one asked more money for transportation, I called the front desk to removed him from the hotel. The hotel was very cooperated and very protective of guest. They even told me not to hesitant to call the security if it happens again or if those guys make me feel uncomfortable. Call the front desk to remove them and never keep up on anything that were not in the table or upon an agreement.