Originally Posted by Zeus

You don't specify which car model?

Aftermarket cats on a Benz, esp. a newer model, are a big no-no. Quality and performance are major issues. There is a reason OE cats cost $800+ a side. Materials, (semi) precious metals, ceramics, etc.

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Unfortunately that's not really true. The cost o fthe cats are driven by those items, but the total cost is much, much lower than what you pay. The price the customer pays is determined by what GSP (Global Service and Parts) thinks the market will bear plus the exorbitant markup charged by your stealership.