There is a difference between the prices on our "Buy/Sell" feature and the market price. This is called the spread.
Typically, the spread centers on the market price; in other words, the market price will be somewhere in the middle of the buy and sell price.
The price at which you buy will always be higher than the price at which you sell your cryptocurrencies for on Buy/Sell. Additionally, because of the spread, the price you pay/receive will be slightly different to the market price.
In times of high volatility in the market, this spread may increase due to the rapid price changes. Additionally, the nature of the coin itself (in particular low volume coins) can also have an influence on the spread.