So there are many places to buy and sell bitcoin, some places like Mt.gox always sell around 30 bucks higher than coinbase. So what if we buy from coinbase and sell at mt.gox, isn't that a huge exploit?
Again I'm sure this was thought of but, could someone please explain?
It's called Arbitrage and highly profitable if you can make it work. It's actually needed in order to keep all the exchanges up and running. I think when you explore your options in doing this that the problem is with moving fiat around.
If you buy low on one exchange sell high on another you have to extract the fiat so you can repeat.
Since extracting fiat o MT Gox is near impossible if you are in the US, you'll need to solve that problem.