These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Game Breaker: Buying tons of a Level 1 unit (>100), upgrading it the point where selling just a few pays for the next upgrade (somewhere past 10), then selling them in mass will net you a huge amount of cash. Easiest to do on 100K mode.