...I used a 10% off coupon we received in the mail. As the lady handed me the receipt, I saw that they gave me 5% off instead of 10%, so I asked about it. She said, and I kid you not, "Oh, no - it's 10% total - 5% off parts and 5% labor." It took me a few minutes to convince her and the owner that that's not how percentages work, but they finally got it and were cool about it. They handed me cash out of the drawer, which still didn't quite total the full 10% discount, but I wasn't going to haggle over a dollar and some change.

I'm hoping it was just an honest (yet alarming) math mistake, rather than an underhanded use of false advertising. They've been sending me these mailers for quite a while, so I'm kind of surprised no one else has called them on it before.