There is a curious feature of EVE Online's market. Occasionally a capsuleer will buy a product and instead of the seller getting the ISK it will go to to a different industrialist selling the same item in the same station. This stock switching only seems to occur when cheaper stock is sold in place of an identical item selling at a higher price, and may have something to do with synchronisation times when near-simultaneous buys are made, but I don't know.
The curious situation happens to me occasionally, where I'll find some of my modules have sold for a little more than their listed price. Because when it happens I am always credited with more ISK than the modules would normally sell for I really don't mind, generally appreciating the extra pocket money to save up for an Orca a few hundred ISK at a time, and as it is an entirely passive process I hardly think I can be accused of taking advantage of an exploit.
However, when the extra ISK I inadvertently acquire runs in to the millions sweat starts forming on my brow as my eyes bulge in sympathy with my wallet. Logging on to find a bug jump in the ISK in my wallet I naturally assume that I have been given my share of profits from the current wormhole operation, particularly as loot has recently been shipped out to high-sec to be sold. But my wallet's journal doesn't show any corporation payouts, although there is a suspiciously large market transaction in my favour to shed light on my gain.
When I put my last batch of missiles on the market there were some already listed that obviously had an error in their price. Instead of listing the missiles at, for example, 43.98 ISK each the decimal point had been carelessly omitted and they had been put up for sale at 4,398 ISK each. Needless to say, I wasn't particularly worried about these missiles encroaching on my business and paid them no mind.
It is then a little unfortunate that when a capsuleer tries to buy some missiles the higher price gets credited to my account, presumably also meaning he gets charged that amount for the purchase. This is how I end up making twenty million ISK from the sale of five hundred missiles. It is a splendid little windfall but I hope I don't get in to trouble because of this. I didn't do anything!