Every sentence forces you to say who you are relative to the other person. This isn’t politeness on top — it’s the grammar.
Your Vietnamese
The same scene, six ways
You want to buy something and haggle a little.
The dialogue
The social setting
you say em
you call yourself anh
You're the elder here: you're the one who doesn't get the deference. No respect marker on your side — adding one would ring false.
you
Anh muốn mua cái này, em ơi.
I'd like to buy this.
the other
Cái này năm mươi nghìn.
This one is fifty thousand.
No slot at all: a sentence can perfectly well carry no pronoun. That's the avoidance strategy (§5.2), in the wild.
you
Bớt cho anh một chút được không em?
Can you do a bit better on the price?
the other
Bốn lăm nghìn thôi, anh lấy đi.
Forty-five thousand, go on, take it.
you
Anh cảm ơn em.
Thank you.
The reference dialogue of §6.1: one sentence, six outfits.
If you don’t know
A course teaches you the right answer. In real life you’re unsure — and saying nothing costs more than getting it roughly right.
Asking someone's age is fair game
In Vietnamese, asking someone's age isn't rude: it's necessary, because the language needs it before you can pick a term of address. Vietnamese people ask early, for exactly that reason.
Cho em hỏi, anh bao nhiêu tuổi ạ?
May I ask how old you are?
Doing without a pronoun
Vietnamese lets you drop them. A sentence with no pronoun is perfectly grammatical, just a little neutral. That's the fallback when you don't know: you speak without placing yourself, you watch, then you line up.
Muốn mua cái này.
(I) would like to buy this.
Listen to how they address you
The single most efficient rule in this module. If they call you em, they consider themselves your elder: call them anh or chị. The information is almost always already there — this is a skill of social perception, not of memory.
Getting it wrong is survivable
Foreigners get a lot of slack. Saying so out loud lifts most of the anxiety that stops people speaking — and staying silent costs far more than being approximate.