It depends on the following 2 scenarios:
If a seller hires an agent to sell the house, the seller normally pays the agent 5% of commission. If a buyer has no agent, the seller agent can get all 5% of the commission. If the buyer has an agent, then this buyer agent normally get 2.5% from the seller agent, which means the 2 agents split the 5% commission.
However, if the seller sells the house himself/herself without hiring an agent, and if a buyer comes with no agent, the seller can save 5% of the commission. If a buyer comes with an agent, then the seller will pay about 2.5% commission. Of course the seller prefers the buyer to come without an agent, to save the commission fee. That's why the seller has more room to give discount to the buyer when he comes without an agent. 所谓羊毛出在羊身上。