I see people all the time quite convincingly saying (with a friendly, disarming smile) "oh no, it's no problem at all!" when in fact it is a problem, they don't want to do whatever it is, internally they're distressed. But social conventions (of varying power depending on the culture they grew up in) are forcing them to say "yes", and do it convincingly.

It's actually easier if someone demands a favor and they are obviously rude/inconsiderate about it; it's more "okay" to respond to rudeness with a refusal or excuse.

But some people are unable to say "no" to polite requests for assistance even when they have to lie to accept convincingly. Even if it's hugely inconvenient for them, and only of minimal benefit to the asker. So they say "yes", and probably do whatever it is, and then will try to find a way to avoid the asker in future (don't pick up their calls, etc).

There's some argument that everyone would benefit from a more "American" (ideal, not always real) and more direct approach -- e.g., someone asks "would it be easy for you to..." and you answer "sorry, no", and no one is upset. But this is next to impossible in some cultures, and there's also value in (if you're the asker) putting more thought into how you can value other peoples' time more accurately.