While Midas is a chain, they are indenpendently owned and operated, so one might be bad, the next good.
I've only had recent experience with one Midas shop, Columbus, Georgia, where I grew up. I had them replace the muffler on my '88 Jeep Comanche about ten years ago. A couple of years later I was rearended and the tailpipe was bent and the muffler damaged by the tailpipe being pushed forward. I took it back and told them to replace the parts. They refused to charge me for the muffler or labor on the muffler, just for the tailpipe.
More recently, about five years ago my '91 Ranger four cylinder needed a muffler, I went to them and they replaced the muffler and tailpipe full of holes. Just a couple of weeks ago, while changing the clutch I discovered the muffler inlet pipe was rusted loose from the muffler endcap. this is five years and right at 150K miles later, they replaced the muffler, tailpipe was fine. No charge, zip, none. The warranty says I have to pay labor to replace the free muffler, they said they don't charge the labor fee on warranty replacements.
Charles