I was once involved in a retail food establishment. People would come back and say “I bought ____(insert item here) for a party and it was terrible. Nobody was able to eat it”. If you asked them what they did with it “Oh, I served it anyway” usually meant they were just fishing for a credit or refund. If however they came back with half a ___ you knew it was a truly valid complaint.
With any retail establishment (especially food) the best practice is that “the customer is ALWAYS right” whether you think so or not, and just do whatever you can to placate them.