[cdru]

It may be the same quality. The eBay version may also be a cheap knock off with inferior quality. The muffler shop is going to have a higher markup then an eBay store as the brick and morter shop has higher expenses. Same reason why you can find cheaper computer gear online then at Best Buy. The muffer shop's price may also include labor (or a reduced labor rate). Be sure to compare apples to apples and not oranges to kumquats.

And don't buy a muffler for the "little boost and the little better fuel ecomony". Adding this muffler to a otherwise stock exhuast system will do nothing for boost or fuel economy.