Think it has caught a few people out. The main issue at the moment is you have to be onboard the carrier to transfer fuel from the cargo bay to the fuel tank. Would be great if the crew could do it for us remotely. Not quite sure what I am paying the Tritium officer for, in his screenshot he looks like he's snorting the stuff.
Regarding your buy/sell test. Sounds like you where just moving credits between yourself and the carrier, I doubt any exploit is involved.