NPC Credit Limit.
Apparently the code isn't as smart as I thought.

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.

I can't be beating people up unless I build a combat character, so that's sorta unfair to those of us with other skills and builds.

You can get cheaper rubber duckies by different means. Best prices take RP.