I'm quite happy if they say "no" because it indicates that they weren't pressured by the request.
I was brought up with the concept that, "it never hurts to ask", but if someone always says "yes" then I'll stop asking that person for favours because I will fear that they are someone who feels obliged to help when asked. Conversely, someone that says "no" I'm happy to ask again in future, because they are answering honsestly whether or not they are prepared to help at that time.
My concept is to ask and expect a "no". That way if you get it a "yes" it is a pleasant surprize.
I'm also one that would often be happy to help but reluctant to offer for fear of offending the other party. So I'll ask for help but I'll usually not offer unless someone is in a rather desperate position.