Speaking with power to create sales

Everyone of us has to speak in public to "sell" something. It may be how you earn your living such as a business development role or sales representative, or that you have an idea, a suggestion or proposal that you want someone to "buy in to". It could be that you simply want your spouse, partner, child or friend to agree to something you would like them to do, but in any event you are selling a concept, an idea - you are looking for agreement.