Hi My wife and I will be traveling to Vietnam in mid October. Entering in Hanoi and eventually end up in Ho Chi Min. From Ho chi Min we may decide to travel to Cambodia for a few days and come back to HO Chi Min and fly home from there. We will be in Vietnam a total of 29 days. IF we get a single entry visa but decide to visit Cambodia and return to Ho Chi Min once we are there, would it be difficult to re-enter Vietnam to fly home. Would we have to buy another single entry?
We suggest that you go with multiple entry visa from the beginning to cover your trip to Vietnam and your entry from Cambodia, that would save you more time and money.
However, if your travel plan is not yet confirmed, you can apply for a single entry first, then get another single entry while you are in Cambodia.
Hope that helps!