Just reading your responses I'm wondering would you feel the same if you were that last minute passenger? Would you be ok with me checking yours bags?
We try to encourage small bags to be place under the seats so we can place larger bags in the OHB, that way we can get as many bags as possible in the cabin.
As far as refusing to move your computer bag from the bin because you need the space under the seat, that is fine by me. Once again just keep in mind you will cause someone Else's luggage to be checked and placed in the cargo bin. Now they are going to have to go to baggage claims and wait for it.(
and Like I said this could be you) they most likely will not be too happy with you, so when they start some beef with you, don't come running to me for help. Just tell them you know Scott and see if they care.
