Scam Artist Waitress from Hell

Allow me to share my chagrin over what happened to me at Le Gamin on Houston Street yesterday, a place I have frequented in the past, but will no more.
I ordered a crepe confiture, which means a crepe with jam or marmalade. The waitress brought me a crepe with fresh fruit. I said that this was not what I ordered. I have ordered the crepe confiture many times before and it is always made with jam. She insisted I was wrong, even though I said that I knew what confiture means in French. Still pretending I was a moron, she assured me that confiture means fresh fruit. I asked if she could exchange it, she said no. Impossible. I said she had to because that was not what I ordered. She went to the kitchen and brought back a tiny dish with jam on it, so I could do it myself. I said that was unacceptable. She then instructed me to go tell the cook what I wanted. As I foresaw, the cook was Mexican and indeed he told me that the confiture crepe was made with jam and promptly made one for me. Which leads me to believe she deliberately gave him the wrong order because the fresh fruit crepe is more expensive.
Then we asked for the check. On a 27 dollar check there was a 2 dollar unexplained charge and a 4 dollar tax. We told her she had overcharged the tax. Then she explained that the numbers were switched around, the tax was 2 dollars and there was a service charge of 4 dollars. It seems to me this woman was trying to rip us off. Usually, most people figure out the tip by doubling the tax amount.
I don't know why we left her a tip. Because I am a decent person and because the custom is ingrained. If there was a 4 dollar service charge, then that should have sufficed.
But what really makes me want to employ violence against this harpy was the absolute nonchalance with which she insulted our intelligence.
And I wonder if she's just a bad apple or that is the house policy, to mistreat and scam the customers. There was no manager on duty.