It happens more than you would think.
Yesterday, one of the sales ladies wrapped up a customers $3000 purchase, put it into a lovely gift bag, and sent him off smiling - Shopping done!
About 15 minutes later I was doing something and commented that someone had left a diamond bracelet in the ultrasonic cleaner. She turned white. Seems she put it in the cleaner and went to cut the paper for the box. Got distracted by a phone call and came back and wrapped the empty box ( we were swamped with customers). We luckily dealt with the whole family, and called the son to get hold of his dad. He brought it back and we re-wrapped the box ,with the bracelet in it this time. He was a good sport, but it could have been a disaster.
I have heard a version of this story from almost every jeweler I know.
Stacy