Whenever I got overpaid I knew it and didn’t spend the extra. I held it until they discovered it and took it back.
In my case, I had just finished jump school and because of an Army experiment was sent to a leg unit (9th Infantry Division) to train recruits straight from basic instead of sending them to AIT.
I kept getting jump pay which I thought was supposed to end after 90 days but it kept coming, I went to finance about it and was assured it was correct, I went to finance a few more times and every time was assured everything was correct, I finally assumed that there was some technical army reason related to why I was there to train the OJT guys instead of having been sent to the 82nd like I wanted, and then one day, all pay stopped.
In 1972 I needed every penny I could get to survive off base yet I had tried everything that I knew to make sure I wasn’t getting in a hole and the finance people were all 100% sure I wasn’t.
Same only a pension payment. I was told in advance what it would be, I stated it was double what it should be and had everything documented in emails in which they insisted they were right and I was wrong. 6 months later they told me they made a mistake and wanted the overpayments returned. It was in a bank savings account so no problem.
Folks should know what they are getting. The government is clueless.