My truck had an awful sounding exhaust leak. Another mechanic told me it was a bad doughnut flange and quoted $100 to fix. Thrifty Muffler pointed out that my particular truck's exhaust system didn't even have a doughnut flange, and that the problem was only just a few loose, rusted bolts that required some torch heat to get tightened down again to stop the leak. $10 to fix at Thrifty. Done in less than 15 minutes! Awesome.