This scam has been widely publicised locally and in Thai and international media. Despite this many people are still unaware of the problem. Others may not realise how much of a problem it is. The scam involves damage caused (whether actual or pre-existing) to jet skis while they are on hire.
What happens is that a foreigner hires a jet ski. On return the vehicle is checked for damage. The damage may have or may have not been caused by the hirer. They are then set up for an extortion bid where a disproportionate amount of money is demanded. The hirer may be threatened either actual or implied by being surrounded by a group of Thai men. Most people just pay to get out of an ugly situation.