On Sunday, I was on a flight in Greece, on a A320. I was sat just forward of the wings. Someone sat in the isle seat opposite me, asked if she could move to the back to sit with her friend, since the seat next to her friend was free.
The cabin crew member said she'd check with the pilots, as the flight was almost full and carrying maximum fuel... strange. She then returned and said she couldn't move seats as it would affect the 'balance of the aircraft'.
I find it hard to believe a roughly 200lb human could affect a 183,000lb aircarft in any tangible way, but I wanted to ask if this would be a real reason for declining such a seat change?