Most people try to be persuasive by giving a dozen reasons to buy their product.
Often it is the non-verbal things that are the deciding factors for your audience. People tend to buy from folks who appear confident.
The way to look confident is easy; have good posture, make eye contact, smile, speak in a strong voice and don’t be afraid to move your hands and arms.
The more confident you act, the more likely they will buy whatever you are selling.