I actually got a write up for a similar situation when I worked retail.
Guy claimed he gave me a $50 instead of $20 for his dvd purchase. He screams and throws a fit loud enough my supervisor runs over and tries to handle it.
They point to a camera above the register and say they'll watch the recording, they walk out of line of sight and instantly are on the walkie telling me to give them the $50 change and they'll deal with it later.
I tell them I'm not doing that and if they want they can come log into my register and hand the money over. They fought it for a minute but realized I wasn't budging until it was them handing over the cash.
The supervisor comes back, logs in, and hands them the cash while I have two coworkers sign a piece of paper I wrote up, under our camera, stating they saw the supervisor give the change to the customer.
Supervisor took me to the back and said I was being unprofessional and not following directions so they wrote me up.
Later that night my til is short so loss prevention and the store manager take me to the office saying they're going to have to fire me.
Thankfully that paper and the cameras saved my job, but that supervisor was demoted and transferred. I had to call HR and get into quite a fight to get the write up overturned.