This happened about a year ago but I just remembered it.
I'm a fresh Low rank supervisor at a national pharmacy chain. Every couple weeks we have amazing deals on certain things in the store and of course the coupon ladies come out big for these sales.
So one time we had half gallon jugs of Clorox Bleach on sale for $1.99 (This is just a guess, I can't remember the exact price.)
A woman comes up to the front register with every bottle we had on the shelf, along with a coupon for each valued at $4 off one bottle.
She's arguing that we had to give her the overage in cash back, my manager's trying to explain that that's not how it works, that she's only supposed to use one coupon per transaction etc etc.
In the meantime I noticed that the coupon was printed at home, and the ones she had looked like photocopied ones at that. Mind you I use coupons.com to print my own coupons and I'd NEVER seen one this good. Then I saw that the coupons had a QR code on them and on a hunch I pulled out my phone's barcode scanner.
Me: Ma'am I'd love to help you redeem this coupon, mind letting me scan it to see if there's something here that can help us?
DC (Dishonest Customer): Sure go ahead.
I scan the QR code which brings up a coupon verification website
Me: Well it seems I found the problem, while this barcode is indeed a coupon for $4 off, it seems to be $4 off Jennifer Lopez Perfume and not Clorox Bleach. I'm afraid I'm not going to be able to accept these coupons at this time.
Of course here comes the inevitable diatribe about poor customer service, calling her a liar, calling her a thief and this one was fun it devolved into her telling me that I was racist. Yep that's it 100%, I protect my stores assets with my amazing racist powers. Not my ability to see that some things that are too good to be true usually are.
BTW: My store manager was in the process of manually applying every coupon to her bill before I discovered the malice involved.
Anything to not get a complaint with this guy. No spine at all.