You can verbally OK on the buyer agent verbal offer, but have written offer sent within requested the time because verbal OK means nothing unless the offer document is acceptable on contingency, down payment , buyer funds and more. The seller agent can counter offer , if the offer is close to the offered price or reject or let it expire or accept. Have no ego, but play with the rules because I was seller one-time and been through Buyer/Agent unprofessional approach. Most serious buyer/agent will work with you, but those unsure will run-away from sending written offer. It is always good to check for lender approval and financial information by Seller and Seller agent before Buyer Agent and Buyer visit your house and have them visit by appointment unless you have vacant house for sale.