There are things it’s considered rude to ask for. Sometimes it’s also considered rude to say no to some rude requests. Sometimes it’s considered rude to even show annoyance or reluctance.
This means that you can’t always tell from someone’s reactions what they are and aren’t ok with. So it’s important to think about it, and make a good guess about how someone is likely to feel before you ask them.
Sometimes you will make mistakes about this. That’s ok. Everyone makes these mistakes sometimes.
There are no hard and fast rules about what it’s polite to ask for and what it’s polite to say no to. It depends a lot on your particular subculture, and your particular relationship with the person you’re asking.
Some things to consider:
Think about how intrusive the favor is likely to be. Are you asking someone for their time? For something that will reduce their privacy? For something that could be risky, painful, or embarrassing to them? For resources? How are they likely to feel about that?
How hard or easy is it for them to say no? (It’s usually not so hard for strangers to say no. It’s much harder for friends and family.)
Have they indicated willingness to do that kind of favor? (Eg: if you’re looking for people to stay with, it’s rude to ask random strangers on the street. It’s not rude to make requests on couch surfing sites or to ask a conference that has offered to arrange home hospitality for help finding a host.)
Reciprocity is important. It’s often rude to ask a friend to do something for you that you wouldn’t do for them. (Eg: if you wouldn’t let a friend stay with you, it may be rude to ask to stay with them.)
Reciprocity doesn’t have to be doing the exact same thing. But it does usually mean being willing to help your friends in comparably significant ways.
(Eg: if you’re never willing to do significantly inconvenient things for a friend, it’s probably rude to ask to stay with them.)
It’s important to acknowledge favors. Saying thank you to someone who does you a favor makes it much more likely that they’ll feel good about it rather than resentful. Even if you’re sure that they know how you feel, saying thank you is usually important.
This isn’t an exhaustive list. There are a lot of potential factors in whether or not requests for favors are likely to be welcome. No one knows all of them. You don’t need to know all of them. The important thing is to think about it seriously and make your best guesses.