Although this is well known in Bangkok it now seems the scam has been exported to HCMC. This is the first time I have heard of it in Vietnam. I've only heard of lone males being targetted. Here's how it goes....You are talking to a friendly guy in the street. He asks where you are from. You tell him your country and he then, showing surprise, tells you he has a sister/daughter who is going to visit/work/study in your country. He is very genuine and sincere and knows a lot about your country (maybe he says he is a golf trainer and can list a few top names from where you come form). He then asks you if you would please come back to his house to speak to his sister or the mother to let them know more about the country/reassure them.The taxi is paid for and maybe some food is offered. If you are male then maybe even another girl in the family starts some flirting with you. The girl who is going to your country isn't around but will be back in a while.While you are waiting somehow the conversation will get to playing cards and someone will amaze you with some subtle ways at cheating at cards. After a while (maybe a beer, more flirting etc) you will be encouraged to join a rigged game so you can help win a lot of money in a risk free game. From there you will lose a lot of money if you decide to proceed.In the end if you don't gamble you will be introduced to some details about a sick child and asked for a donation which will be put in a sealed, signed envelope.This scam works because it seems very genuine to start with and you also feel very reluctant to not help out someone who is going to visit your country. After that you feel embarrassed about not wanting to wait, help win them some money by gambling after they have paid your taxi and given you snacks and drink. Then you would seem totally cruel not to donate to a poor little boy.