There is a lovely English question that Vietnamese cannot translate concisely: What's the catch?
It asks: is something being hidden here? What condition comes attached? What is the real price?
Why Vietnamese struggles to match it
In Vietnamese you have to ask about each thing separately: "Is there a fee?", "Do I have to do something in return?", "Am I tied into anything?"
What's the catch? contains all of those at once, in three words.
It earns its keep in business
Someone arrives with a wonderfully attractive offer: you get this, you get that, I will handle everything.
The question to ask is: what's the catch?
Because there's no free lunch.
Two real examples
A food delivery platform. They say: sell through my platform, the app is excellent, you will get far more orders.
But the catch is you give them 30% and you get locked into the platform.
A flat to rent. Good location, fully equipped, surprisingly cheap. So, what's the catch?
The catch is you've got to pay six months up front.
Its natural companion
If something is too good to be true, it probably is.
Learn these two together, because they turn up in exactly the same kind of situation.