One of the key differences between a prediction market and a traditional betting platform or sportsbook is that there is no "house." The odds are determined by the users and we're doing our best to make odds as transparent as possible, but there is always the chance that ,as you say, some last moment whale could swoop in and swing the odds.

Proper market creation can significantly limit this issue, which most of the newer markets have been made stronger than the few initial markets and help avoid this. Making sure that the market closes with a significant length of time before the outcome of the event can be known is key to prevent the behavior that you are speaking about, so it's up to the market creator to make a strong market and the oracles to invalidate markets that don't seem fair or to be working as intended. When a market is invalidate everything returns to the users and the only expense incurred by anyone is the market creator's burned PAL, which encourages them to make better markets.

You've provided some great feedback here and we're continuing to develop the site to try to make odds easier to read and educate market makers and oracles on creating fair and interesting markets. As the userbase grows and volume increases the odds should be much less volatile. Thanks for checking out the site!