1st interview seemed thorough with a very friendly interviewer, then I was transferred to their Ex-Pat manager who made me an official job offer. I accepted and began planning my life based on this offer. However, after some three weeks of emails back and forth, I raised some concerns based on the common themes in the poor reviews here on Glassdoor, and they promptly rescinded the offer saying: 'reading between the lines, it's clear that you don't want this job' and that they had already offered the position to someone else who would be more 'grateful'. That was pretty depressing. I simply asked for clarification on changes to their 'relocation assistance' package, if I could talk to my future manager ahead of time, and why they had not yet sent me a copy of the contract -I was unaware that Vietnamese contracts need to be signed and notarized in Vietnam, or else they are invalid. This was not made clear to me, and is the first country I have known this to be the case.
This cursory, sudden and callous rejection -for taking time and asking questions- has left me greatly inconvenienced here at home, having given up work and my current flat on the basis of their initial offer, leads me to suspect that you should pay attention and give great credence to all the many complaints here on this site.
Maybe I dodged a bullet, all I can say is they will not hesitate to back out of their commitments, so I'd advise you to purchase a refundable ticket, if possible.