The full list of costs that come off the top
Real estate commission, legal fees, any agreed adjustments at closing (property tax proration, for example), and whatever repairs or staging were needed to list competitively — all of it reduces the number that actually lands in your account.
Why comparing headline prices to a cash offer is misleading
A listing price and a cash offer aren't measuring the same thing — one is a gross asking figure before costs, the other is typically closer to the net number you'd actually receive. Comparing net-to-net is the only fair comparison.
What's actually negotiable
Commission rates are negotiable between a seller and their brokerage — ask directly what's included in the fee and whether there's room to discuss it, especially for a house likely to sell quickly.