what do you mean by "non-existent coins"?
I mean coins that were not ever mined but only existed as credits into an account at Bitstamp.
Like gox coins. I don't understand how everybody thinks gox pumped the price, when instead they were selling non existent coins en masse, Logic says this keeps the price down, because they were flooding the market with coins that were not there (naked short selling).
Gox coins did not pump the price. Mark Krapeles pumped the price only when his dishonest attempt to hide his lost coins resulted in him buying coins (via willy bot) to continue the ruse that he still had them and that MtGox was still solvent. This only drove up the price on Gox which is why there was the large price disparity between Gox and other exchanges. Why that guy isn't in jail yet is a mystery to me.
Incidentally, I got my coins out of Gox when the price disparity became suspiciously large. Just in time as it turns out. It's generally a good idea to play it safe whenever you smell funky kicks going down in the city.