Look, we all make mistakes. When you have experienced talking yourself out of a sale, "get back on that horse" and sell again. And don't think you will never get another shot at the customer you blew it with. In fact, I would suggest you contact them again to see when you might be able to revisit their needs and expectations. If necessary, ask the customer to forgive you about "getting pretty darn excited about your firm's strengths." Many customers will appreciate your honesty and welcome you back.