How do the various exchanges determine the price? Whats to stop one exchange selling at $5000 and another for $3000? How do they synchronise their pricing and why do they differ slightly?
Just want to add another point for this. If such thing happens (either one exchange is overpriced or underpriced), then some traders will use that opportunity to buy/sell their Bitcoins to get some profits. After that, if the liquidity is enough, the price will eventually come back to the market price (same as other markets).
Most traders won't use an exchange with very small liquidity. So even if that arbitrage opportunity exists, the risk would be greater than the benefits, and the exchange will eventually cease to exist.