its really an issue to do with the airports not the airlines and definitely not the poor check in staff!
It's that kind of SLF myth that means that this issue will be with us for ever.
The airline that takes your money for excess baggage, either itself or through its appointed agent, IS RESPONSIBLE for not defrauding you with incorrect scales.
IT IS A FRAUD THAT EARNS THE AIRLINES MILLIONS.
The airport often supplies the equipment, and should be made responsible to the airline for its proper functioning via its contract between the airport and the airline (or agent).
Nothing, nothing in those arrangements, whatever form they take removes the airline's responsibility for not defrauding its customers.
The fact that no-one, not the airline, nor the agent, nor the airport, nor the police standing around doing SFA, no-one, is the slightest bit interested in ensuring that passengers are not defrauded is evidenced by the fact that testing the scales' accuracy can be done in 10 seconds with a calibrated bag of known weight, ideally 20Kgs, kept ready near the desks and used daily. I've instituted that wherever I was able to do so. It's very easy.
If that were common practice this vicious and lucrative fraud would be wiped out overnight.
I write as an ex-airport manager, handling agency manager, and airline traffic manager. This scandal has been going on for decades and needs to be stopped.