I worked with a lady who was skimming on paper purchases. Every week, she picked up supplies on her own credit card, including 10 cases of paper at about $30/case. She brought six cases into the office and left four in her car/van, which she would return for a refund two days later, processing the original receipt on her expense report.

I think she did this for about four years, so she was skimming about $6,000 a year.

It was only noticed after she left and her replacement kept buying the "usual" order of 10 cases of paper and the storeroom filled up with too much paper. This led to a call to the supplier to said, "Well, she usually bought 10 cases, but most of the time, she returned 4 cases by mid-week."