[lrajlich]

If you plop a big limit buy order at $26.40 and the market's at $26.20, you will wind up paying close to $26.40 because you'll eat through all the sell offers and transact inefficiently. It's called slippage.

However, what's preventing you from getting f*ed is that this is a market, so basically you have 10+ HF shops fighting who can be on the other side of that slippage. The fact that it's a competitive market ensures you don't get raped like the guy claims.