I question the integrity of a muffler being sold at a Buy It Now price of under $20! Is it just a coffee can with an inlet and outlet?

Most muffler shops will weld tips on for little cost. The guys you talked to wanted to sell you something, so they quoted high to make you go away!

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car