NYMackem
Striker
This has been my experience. No measurement of shoulder bags slightly over size, but you'll get hooked for a wheelie case. Airline dependent too - Ryanair are much sharper at extracting every penny than the other low cost carriers, and no national airline I've flown on seems to care at all.I haven't paid a charge yet with a cabin bag that is over the limit.
The people they tend to stop are people with more that one bag or people wheeling their luggage.
They gate staff normally look down the line for likely suspects and people with modest carry on stuff are OK.
My ruck sack is a few centimetres over in every direction, but it's never packed so could squeeze into the measurer if needed.
Saying that, rules are rules and if you get caught, just pay the 50 euros and divide it up against all the flights when you haven't been charged.