Bitcoin is just like any other thing in the world, if you want to to buy a car you will realize there are several prices for the very same model and the same is true for bitcoin, different exchanges have different prices at any given time and all of those prices are real, if you are a trader make sure to buy from the exchange that has the lowest value so you can buy more bitcoin.
Yeah most of the prices indicated in established exchanges are often reliable though they don't have the same price. Though i don't recommend buying from one exchange then selling on another. Fees would likely level the difference and you might lose a good opportunity while transfers are being done.