Whenever you place an order, we give an indicative price based on the current market data we have available at the time. While executing your order, we get quotes from multiple financial sources to ensure that we get the best price possible for you.
If you have a "Market Order", it will display the best ask/bid when you place the order, and it will execute at the best ask/bid price remaining once the order is processed. The risk is that the price at which your order executes will be greater than displayed.
If your order happens to be a "Limit Order" it will be triggered only when a specific price is reached, and it may execute at a better price, charging you less to complete the order.