Revealing mistake: When they are burying the Swede on the beach, you can see him blink when they throw sand into grave.
Revealing mistake: Take a good look at the crowd of backpackers waiting outside the office in which Richard just has been questioned by the police. They are the same people that later in the movie are welcoming Richard to their happy, secret paradise island community.
Chosen answer: It's Ko Phi Phi Leh island off the coast of Thailand. It's a protected area, off the beaten path, and tourism is discouraged. There are resorts on nearby islands.
rswarrior