I had a dispute with Canada Revenue Agency and won. A good part of a decade ago now, I got into contracting for a couple of years. The accounting lackeys at S_____ W_____ in Richmond, BC, Canada paid me using cash method accounting. They marked down payments to the date they actually paid. That was often late, so for instance December money would end up in January, and since that's when the money changed hands, it was now next year's income. They reported it this way to the CRA (unbeknownst to me, who would not suspect such a practice at this level of business). In one year, November and December payments were paid in January, and accrued to that year's income from their side.

In my self-made accounting system, written in a self-made Lisp, I used accrual accounting, associating all transactions with their correct dates, and remitted taxes accordingly.

This resulted in some amount owing (looking like underreporting).

I used reports from my accounting system to document my case, and they agreed with me: I did my accounting and reporting the right way, and that company should not be using cash-based day-money-changes-hands accounting.