Mrs. CPT and I travelled to JNB on firm full fare D class (discounted business class) tickets as it was a business trip but through an oversight our son who was then 3 had a standby economy ticket issued by the company travel department.
There were >100 seats available on the flight (happy days!)
When we got to FRA we were screamed at by the gate agent who said : "Zis ist against ze rules ......" and when I asked why she told me : "Because it is against ze rules and zat ist vy!"
She said : "Vat vill happen ven zere is no seat for ze boy?" I explained that we did not expect him to travel in business class, one of us would travel in economy with him, and if he could not get on at all (unlikely) one of us would stay behind with him.
After another 10 minutes screaming at us she handed us our boarding cards : 2 business class for him and his mother, and 1 first for me!
Another time I was on standby for CPT LON on SAA, more than 100 seats on the flight, and the check in agent refused to accept my luggage until 20 minutes before departure 'in case there are 'goshows'.