A stock exchange's job is matching a buyer's price with a seller's price, continuously, thousands of times per second — the mechanics behind that matching determine what price you actually get.
The Matching Mechanism
Every order carries a bid (the price a buyer will pay) or an ask (the price a seller will accept) — the gap between them is the bid-ask spread. Market makers (at Nasdaq) and Designated Market Makers (at the NYSE) are firms obligated to keep quoting both sides, providing continuous liquidity even when public buy/sell interest is thin. A market order executes immediately at the best available price; a limit order only executes at your specified price or better, trading certainty of execution for price control.
For a thinly-traded stock (low daily volume), a market order can execute at a meaningfully worse price than the last quoted price because the spread is wider — a limit order gives you protection against that slippage, at the cost of a fill not being guaranteed.
Someone Trading a High-Volume, Liquid Stock: A market order's execution-price risk is minimal here — the spread is typically a penny or two.
Someone Trading a Thinly-Traded or Volatile Stock: A limit order is the safeguard against an unexpectedly bad fill price.
Trade With the Mechanics in Mind
- Check a stock's average daily volume before choosing order type.
- Use limit orders on thinly-traded or volatile names.
- Understand the bid-ask spread is a cost, even when no commission is charged.
See bid vs. ask price explained and what is an order book for the deeper mechanics.
