Looking at any given stock, I can see top ten Sellers (cheapest first) and top ten Buyers (highest first). Question is.. does the top buyer buy down through the seller list until satisfied, then buyer #2 and so on... or is it less ordered than that?
It can work that way, yes and that's basically what an "at market" order is. There are typically other options you can apply that will change the behaviour. These options will depend on the market, the thing you are trading and your broker.
- Price limit
- Cost limit
- Fill & Kill (fill what you can then cancel the rest without waiting for more sellers)
- Fill or Kill (all or nothing)
- Market to limit (get what you can at the current best price then stop without using up the next best prices)
- Iceberg (has hidden volume that trickles onto the market avoiding showing your entire order up front)
In a perfect world where everything is static, it could work that way. But that's not reality.
As orders are filled, other buyers and sellers come into the market at existing prices or at better prices.
Then there are special types of orders.
In a Fill or Kill order, the entire order must execute immediately or be canceled.
In a Dark Ice order, an algorithm hides the volume displayed to the market by the order.
In an Iceberg order, large volume orders are submitted to the market in increments while publicly displaying only a specified portion of the total order size.
So in short, the quotes that you see may not be what you think that they are.