Have you ever tried complaining at a restaurant? Why?

I remember about 2 experiences. The first one was so long ago. I was eating tasty rib soup, but I found a cockroach in the soup. So I told the restaurant owner and I received a new rib soup and ate it again. The second one was a recent thing. I ordered Bossam in a very big size. But the amount was not very big, so I ordered the very big size Bossam again. After it was delivered, I compared their sizes. They were totally different. So I called the restaurant and got a refund for the difference between the small menu and the very big menu.