回複：回複：回複：合約中，沒有看到可以允許賣主改變主意不賣的寫法

Then tell the listing agent that "If you breach the contract, we'll sue you for specific performance."
Also don't give the seller any chance to cancel the contract, such as demanding them to fix things that are required by the state law. I think it's usually best to hire an agent, because you won't get any better deal if you don't have an agent. If you're really worried and really want this house, consult a real estate attorney.