I often switch my aisle for a middle and I'm usually the one making the request. When we travel as family we book aisle, aisle, window. If someone sits between my husband and son, I will generally offer to trade my aisle for their middle. I was only turned down once, and it was an older woman who said she was afraid of flying and felt safer sitting between two strong men. During a bit of turbulence she was holding both of their hands.