I was watching the trends of a certain stock and the price started to fall, so I purchased. The part I do not understand is the stock price showed $17.30, but when I confirmed the purchase, the price was actually $17.43. What would cause this? Does the bid/ask price have anything to do with it? When I looked at the price chart I never saw an influx in the price from $17.30.

Any insight would be appreciated.