I have a family member (my mil), who always offers up things and then when we take her up on it (which is not all of the time and when we don't she acts unhappy that we didn't), she acts unhappy about it the fact that we accepted it....

So my question...

Why do people offer things they really don't want to offer? Just to be nice? To save face? Because they think it's the "right" thing to do in society?

And when you find out (or figure out through body language and tone of voice) that they really didn't want to offer it up in the first place; do you feel guilty for accepting the offer? How does one handle something like this?