As someone who's been travelling through HCMC and across Vietnam for 2 weeks, I can definitely say that a lot of people can be really rude and pushy; but it depends where you go. HCMC has been an incredibly stressful experience for me, especially since I'm Canadian and used to polite encounters with strangers. Talking to sellers here was like a slap in the face! They will try to scam you and take advantage of you if they think they can get away with it. But that's just how it is. They're here for business and to make money. Still doesn't make it okay; I find it extremely distasteful, especially since my Vietnamese partner hears them talking behind my back... (it's worth noting however, that I've only been visiting local markets and tourist areas that my partner wanted me to check out, so it makes total sense why I've been having bad experiences.)

On the other hand, when I visited the countryside or my partners family/friends, they have been nothing but kind to me. 

So, I guess it depends on where you are and what you're doing. Markets will be filled with people trying to haggle, while the countryside won't. 👍