I was flying last week from STR to AMS, and anticipated an issue with overweight luggage (me and my traveling companion each had checked baggage weighing around 28KG each, above the 23KG limit). We were prepared to ship some heaver items back to the US, but as I checked in, I noticed that business class upgrades were available for about $50 each (we were flying on miles in economy). I decided to purchase them as I figured it would allow for two checked bags per person, plus it would increase the baggage weight limit to 32KG. My travel companion split her baggage into two (two checked bags) while I kept one heavy bag. My understanding is that the heavy baggage fee is $100 per bag, so I figured we saved some money this way.

Upon check in, the agent claimed that as we had only bought a "seat upgrade" instead of a true business class fare that we were not in business class, and therefore, had to abide by the economy baggage limits. I expressed disbelief at this and asked where I could find these terms in my purchase. After a few minutes, the agents eventually checked all of our bags with no extra cost.

Is this a real thing?