Sales people are successful leaving with your money IF THEY HAVE A STRONG WHY to convince you AND ALSO HAVE A STRONG BELIEF IN THEMSELVES.
Would you considered buying a product a salesperson suggested if he seemed uncertain?
They try to be resolved and certain about their cause before they interact with their customers. They do the thinking and they rehearse a list of whys everyday for this reason beforehand.
So I modified a list of whys for you to ask and rehearse everyday in order to achieve a confident mind state when you interact with females and help you being assertive: