Witness this on an UA flight. A pax had a carry-on full of equipment. He took the offer on the free gate check of carry-on as the fight was full. When the agent lift the bag, she realized it was over 50 LB. She charged him the over-weight fee on the bag. Ouch! Personally, I would have a difficult time lifting anything more than 30 LB into the overhead bin. I have seen many pax stood in the isle waiting for some kind soul help them lift their stuffed suitcases. There were always some kind soul to help them out.