It's the classic 'firesale' trick. Bitbay currently doesn't have a whole lot of buying pressure and there's no big buy walls on BTER either. This makes it possible to manipulate the price at very little cost. Simply buy the walls out and set a new price.

Why would anyone do that? It's there to provoke a panic and get people to sell at lower prices. If you can trigger that sense of panic you can get the coins on bargain prices.