Where you do think the money for the commission comes from? Houses aren't a fixed-price good where you declare that you're selling a house for $500k and stick exactly to that price regardless of what you're offered. If a buyer without an agent to pay offers you $490k, that's a better offer than one with an agent offering you $500k if it means you don't have to pay that 3%, and the buyer has saved $10k by not having an agent.