Prices for parts at a dealership are: the actual cost of the part to the dealership, employee price, mechanic price, list price, out of state customer price, whatever they charge local regular consumers etc.

Mercedes Benz has nothing to do with your local dealership when it comes to the price they were charging you. I have bought from several Mercedes dealership websites and they are always the ones processing my order and ship my order. (they never drop ship it is always from the actual dealership) FCP Euro, Pelican Parts, Autohaus AZ will drop ship parts from different distributors.

The prices on your dealership website are for internet customers out of state, that is usually how it works when it comes to dealership websites that sell parts online. They usually have a disclaimer for that on the site or it won't let you order if you are in state.

The parts counter could have charged you the list price but that is not what they charge customers like you that walk to the counter. My local Mercedes dealership will sell me parts at the actual list price but a few years back they were marking up everything way above the list price. All 3 local Chrysler dealerships give me different prices where one charges twice as much as the other two.

In my experience, you can sometimes ask the parts counter if they will sell you the part at the list price and sometimes they have that discretion and sometimes they don't or simply refuse to.

I miss oediscountparts.com, they were a dealership that sold Chrysler and Mercedes parts with free shipping above $50 but they were sold and the new owner didn't continue to sell parts.