If it's a window for window seat I almost always oblige. But in the past two weeks I've been asked to switch to 1E and switch 1A for 5E. In both cases I paid for F in part because I get the seat I wanted. If a couple really wants to sit together they should do same rather than hoping for 2 upgrades. The switch to 1E request was not responded to very politely by me and they got some poor woman that spoke no English to go along.