A business entity has made a financial error in your favor. The error is not tiny, but it is not so large that it will cause pain to the entity. At what point have you fulfilled your obligation to try to remedy the situation?
How many legitimate attempts would you make to fix the error?
None. It's not your mistake.
I'd tell them once.
I'd tell them twice.
I'd tell them three times.
I'd nag them until it was resolved.
Would you make an extra effort if the size of the error was over:
The size of the error does not matter.
Would you make an extra effort if the entity was:
A small business
A medium-sized business
A government entity
Someone that you regularly do business with
There's some other mitigating circumstance