If you place a buy order you are risking that it get filled in one trade.
Yes. In this form, it's more like a gable than an investment. If things go wild, usually the player with the highest amount of coins wins the round.
Ultimately only someone with inside access to the Cryptsy servers would be able to set up fake buy walls in this manner, and there is no evidence that this has ever happened.
So it covers basically anybody who works there (rogue) + Cryptsy itself (organized).
It's not much but still >0 chance.