So beware saving a penny on the commission and losing a pound on the execution price. It is difficult for the small investor to determine independently whether his or her order was filled with price improvement or not. However, there are several sources on the net for intraday price charts that may help you analyze your fills. On a lightly traded stock, spotting you own trade crossing the tape is easy - and a minor thrill. For many stocks, remember that there are a lot of places it may trade beyond the exchange it is listed on.
Some large firms are trade on exchanges from Tokyo to London.
Domestically, the same is true. A brokerage house can also program its computer to recognize when two orders flowing in from their regional offices make a pairing that can be summarily crossed. Generally, the broker keeps the spread, but some brokers give the advantage to the customer. If there is another order there that mates with yours the trade is immediate - if not, you sit there until that mating order shows up. In either case, Schwab takes its commission and splits the spread with the two customers.