No one would do this
So a couple of intelligent people who have lived in Thailand for many months would suddenly go on a wild goose chase to a country that is closed off from the civilized world to find their son who is most likely dead?
Ok, I'm all for suspension of disbelief and I'm not a father so maybe the idea of grasping at straws is more believable for some, but...if this couple has over 50k USD (I think that's about 1.5 mil Thai baht) why wouldn't they also hire a guide or guides to go with them when they hired on with the shady guy who was going to find their son? NO ONE IN THEIR RIGHT MIND WOULD DO THIS. I went to SE Asia for 28 days in late 2007/early 2008 and just from my small amount of knowledge in what not to do, who to trust, who to avoid, I would never have gone off on my own with people of questionable character on a mission like this. Every guide book, every bit of advice you hear from anyone tells you NOT TO DO STUPID STUFF LIKE THIS. More than likely they would have been robbed and thrown overboard after the first couple of hours.
Why didn't they show a scene where the couple at least told people where they were going, instead of just that one woman who later tried to seduce the husband (she never struck me as the most reliable sort to begin with)? Or maybe a scene where they did hire a couple of bodyguards (if he's paying 50k to find his son, a bodyguard or two could probably be had for as little as $50-$100 per day) to go along with them? Even with the woman's frantic state of mind, I cannot imagine a more untrustworthy person to go with than the freak they met who promised to find their boy. Based on what did he say he'd find the boy? He had no clue, he obviously just wanted the couple's money.
I can understand the people who loved this movie, writing about the cinematography and sound fx, etc., and I agree. It is a beautiful movie to look at. The shot mentioned on one of the other boards in the ruins was excellent. But I could not get over the stupidity of the couple and that, for me, ruined it. Yeah, I know it's a movie but in movies there are character you can care about and stupid people like these are just too hard to relate to.