Originally Posted by
craigthemif
On my most recent flight, a lady had paid for checked luggage but had instead brought her bag to the gate. (standard rollaboard) They wouldn't let her carry it on and they wouldn't let her "gate check" it. (even though our baby stroller was being gate checked so it would have been quite simple to take her bag down as well...

)
IME, cabin crew don't care in the slightest. I rarely pay for overhead bins but I put my backpack up there 9 times out of 10 with no issues. It's only ground staff you need to worry about, and they won't care much about size if you've paid for the overhead bin...
My experience has unfortunately been hit and miss. When they first started the yellow stickers, cabin crew were very much up for enforcing the fact that bags without the labels should go under the seat. Now it's been going on for a while, I think they realise realistically the space isn't needed and you can put your 'personal item' in the overheads.
Side note, no idea why someone would bring a bag and try and gate check it if it's a rollerbags except for the fact maybe they were on a connection with an airline with a nicer baggage policy