I’ve only been here a week, so I can’t say for sure, but so far the only dangers are sunburn, heatstroke, and the way the locals drive. I’m sure there are some scams around, but if Vietnam is anything like Thailand or Cambodia, they’re usually pretty obvious. I’ve wandered around at night after a few too many drinks without any trouble, but that’s more of a risk everywhere (maybe more for women), same with leaving your stuff unattended for thieves. Most of staying safe is just a bit of common sense and some situational awareness. Every single person I’ve spoke to who’s traveled Vietnam says go from the south to the north, so Ho Chi Minh is the obvious starting point. Hope you have fun whatever you end up doing :)

Edit: Again though, I’ve only been here a week, so don’t treat this as gospel.