Client-centric selling means building your sales argument from an agreed upon assumption. If the client or prospect doesn’t agree with the assumption that your persuasion is based upon, then why would they agree with your conclusion?
When you are selling advertising, start your conversation with your prospect by asserting what you know about their business, and what you believe they need. If you are right, they will agree and tell you more. If you are wrong, you need to know that. If you are well-prepared they will be impressed with your knowledge, and listen more attentively.