How to complain correctly
When I worked at McDonald's, we had a customer order an angus burger (the most expensive thing on the menu) through the drive through.
When she got home, she found out that there was no meat on the burger. She brought it back to have the issue rectified, but the whole time, she was very polite to every one she encountered. She did make it clear that she wanted a whole new burger made fresh, instead of just having a patty put on the old bun, but she wasn't rude to us at all. (and as she was saying that, the kitchen was in the process of starting the new burger.)
She was like the perfect complainer. A legitimate complaint, she was funny (in a ha ha kind of way; she was making jokes about the situation with us as she was waiting for her burger,) and never lost her cool. She got exactly what she wanted in the end, and left happy.
The manager did giver her a coupon for a free for her next visit, but honestly, I think she deserved it. She didn't stamp her feet and complain, demand unreasonable compensation (or any type of compensation at all for that matter, except for the burger to be made properly,) and seemed to understand that we are only human, and all make mistakes some times.
True, I didn't server her directly, but she was still awesome the whole time.