

You should look at the External Funds thing mentioned in the article. It gives a different spending breakdown than Purchase History.
Help > Steam support > My account > Data related to your Steam account > External funds used. (Its the 13th item on a huge page full of stuff.)
Now, this is some forward thinking. Straight into the solution! You only have to do this once. Pick the biggest jerk and enjoy it. Draw blood (metaphorically).