As I often travel alone, I am frequently asked to change seats for a number of reasons including 'We want to sit together'. If the person is a passenger and is is polite and the seat is not worse than the one I have, I will change.
If a member of a flight crew asks me to change, I will usually do so as I assume there is a good reason for the request.
As a woman it is often assumed that I am willing to sit next to a child. Not true!