Don't say "yes" or "maybe" when you really mean "no".
There are many who think giving a hard "no" is rude and hurtful, however, often times saying "yes" or "maybe" when you really mean "no" is actually ruder and more inconsiderate. This is because giving a false positive can inconvenience others and/or disrupt their plans, while also just inevitably disappointing them eventually anyway.
Say for example your friend asks you to come see a movie with them. You're not actually interested in this movie at all, but you don't want to disappoint your friend, so you say "yes" or "maybe" when you actually have no plans at all to go to the movie with them. Although you don't want to disappoint your friend, giving them a false positive is actually more rude, because not only are you getting their hopes up, but if you were honest in the first place they could just find someone else to go see the movie with.
Or say your roommate asks for you to pick them up from the airport. You're been so tired and busy lately so you don't want to, but you also don't want to just say "no" to your roommate, so you say "yes" or "maybe" but plan on flaking at some point. You may feel rude saying no, but it's actually more rude to make them think they have a ride from the airport when they don't. If you were honest in the first place they could have started finding another ride from the airport sooner.
Some exceptions apply, such as if you fear giving a clear "no" might endanger your safety. But otherwise, if this person isn't going to hurt you or harass you for saying no, you are doing them no favors by getting their hopes up and eventually disrupting their plans when you flake or ghost at the last minute.
In some places and cultures people will say "sure" or "maybe" with a certain tone or expression that they feel implies "no", and expect the other party to just "pick up on" the fact that they're not actually interested. However, not everyone does pick up on what you're trying to imply, so you are still the inconsiderate one in this case. People can be neurodivergent, or have a different cultural background than you, or have just been raised to be more straight forward and honest. Either way, being insincere with your "yes" or "maybe" is likely to disrupt their plans and cause more disappointment in the long run.
Just be honest and tell them "no" so they can plan more accordingly without getting their hopes up over something that will not happen.
