I had thought the code was able to figure out profit versus pure earnings.
I guess it's not, and in the following situation reacts like this:
You pay 500 for a rubber ducky.
You sell the rubber ducky for 700.
You only make 200 profit on said ducky.
Game thinks you made 700 on the ducky.
Which can make a HUGE difference on how much flash you make on duckies.