Seeing as how the Toyota dealer did such lousy work on your Mercedes there are two things you should consider doing:

1. If you paid with a credit card, contact your credit card company and explain how the work was not only sloppy but completely wrong. The credit card company might withold payment to the Toyota dealer until the situation is rectified.

2. If you didn't pay with a credit card or your card company won't do anything about the situation, contact the Better Business Bureau. They will then act as an intermediary between you and the Toyota dealer to try and resolve the dispute.

Man, I don't know what it is with Toyota dealers. I know a lot of people who own Toyotas, and the local Toyota dealer in my city is always trying to pull something. They recommend work that isn't necessary, accidentally charge you twice for a CEL diagnosis, charge for parts that haven't been replaced, etc. Toyotas are great cars, but I know about several of their dealerships that have very bad reputations.