Another best practice of seat swapping is to immediately explain what the proposed new seat is as part of the initial request. Some people want you to agree to a swap before you find out what the whole proposal is.

Generally I don't mind swapping for a similar seat, but just tell me what the other seat is upfront.

I was flying on a 15+ hour flight on AA once in premium economy with an empty middle seat next to me. Two hours into the flight I'm in a deep sleep and some guy starts aggressively tapping my shoulder and indicating that he wants the seat next to me while I'm still half asleep. Luckily for him I quickly judged that fully waking up to prevent the poaching (he was in regular economy) would have been more disruptive to me than letting him sit down and falling back asleep. 12 hours or so later he went back to his original seat.