I had an interesting experience on the journey to Da Lat, when I forgot my wallet in the bus. I realized the fact only after the bus was gone. A phone call was made and ten minutes later I got the news that they had found my wallet. Immediately a motorbike guy appeared and offered his services for only 150000 dongs (5€). An outrageous price, but I had to catch another bus, so I had to accept it. We went from one place to another one and back. Everybody around me spoke Vietnamese, inquiries were made, I did not understand anything and just followed my guide. Eventually two guys appeared with my wallet in their hands. Their first question was how much money I had in my wallet. To which I told them to just give my wallet back. We argued for a bit, but eventually I got my wallet. Cash card, euros and bahts were intact, but dongs were missing. It was plain obvious from their reaction that they took the money, but words and accusations did not help. Eventually I gave up, hopped on a motorbike and went back to catch a bus connection. This incident produced mixed feelings. One one hand, money was gone, but on the other hand they were honest enough to return my wallet with the rest of the content. Interestingly enough I had more in euros and bahts than dongs, but they did not know the value of these currencies.
I found out that Thai are a nice smiling bunch (at times artificially) and swallow any kind of disrespect, but behind your back they will be sure to express their true feelings. Vietnamese are different. Years of war resulted in the fact that Vietnamese do not tolerate disrespect from tourists. If you offend them, they do not laugh it away like Thais do, but will tell you directly that you are out of line. Tourism industry has created this artificial wall of niceness, where tourists can get away with anything, as long as they pay money. I prefer the Vietnamese way, though. Direct and ruthless, but at least there are no artificial smiles and fake emotions. If they act nice, they are nice. If they act angry, they are angry. Simple as that.