MtGox offered much higher exchange rate than the average market price before going bankruptcy. There are some issues there. They are happy for your deposit,but always find excuses for your withdrawal request. They are manipulating the price. They are dead. I think the value of BTC in a reliable and secure exchange won't depart much from the average market value.
The rate on Mtgox is a lot lower than market price before closing the door and going bankrupt.
It was higher when customer can still withdraw bitcoin but not able to withdraw fiat.
Customers were able to withdraw fiat, it just took a long time. When it took longer then expected to withdraw their money from gox people would panic buy the bitcoin back and withdraw their bitcoin onto another exchange that could deliver fiat more quickly.
The price of bitcoin crashed on gox when customers were unable to withdraw their bitcoin because they thought holding fiat would be safer then holding bitcoin at an exchange with no bitcoin.