[Perfectlap]

^ I agree. And that being said the highest price is not necessarily the best place to do it. My independent has done several hundreds of these jobs and I'm pretty sure charge less for this job than some of the nearby competitors with a reputation for being expensive. I guess I should have clarified that experience is usually evidenced in a higher hourly rate than the nearby muffler shop, but as far as the job itself I'd take note of the number of hours a shop is estimating (should there be no issues) to see if you're getting a fair price. Flat rates scare me a little because that really can be a good thing or a very bad thing depending on the integrity and competency of the shop.
Either way, I would ask how many of these they've done in the past year. The key is experience. One of my mechanics pointed out that this is a job that while straight forward requires someone to be very, very careful. One hasty oversight can lead to big, big problems.