as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
system
where do traders take their prices data from? how can it be different from their brokers'?
user
to add a bit to daniel anderson's great answer, if you want to 'peek' at what a the set of bid and ask spreads looks like, the otc market page could be interesting (note:  i'm not recommending that you trade over the counter.  many of these stocks are amusingly scary):  http://www.otcmarkets.com/stock/acbff/quote you can see market makers essentially offering to buy or sell blocks of stock at a variety of prices.
assistant