There is a lot written about what you can do or say to sell more. Perhaps its better to look outwardly first - at why people buy before making the decision as to what you should do. Understand that and it all falls into place.
The basic theory, as stated by Aristotle (322-384 BC) still has credence today. A huge number of subsequent models from eminent behavioural psychologists such as Eric Berne all support his philosophies and theories
So lets go back some 2,500 years when Aristotle talked about Ipsos, Logos & Pathos as being the drivers to buying. He stated that people make buying decisions emotionally(Pathos) from people they trust & like (ethos). Then they justify that reason logically (Logos).
In other words we buy from our personal emotional heart (to remove pain or receive pleasure) and then we seek a logical justification to convince ourselves & others that the decision is right.
So if you sell, as most people do, on logic and justification - using ROI models and the like, you will frequently fail as it will be a cold and emotionless meeting. Raise emotion in a client and you will win.
Think about how often has a prospect purchased from an inferior supplier or taken a route which is less effective than the one you offer? The chances are that he/she felt more emotionally attached to the other supplier or their solution than to you.
We can all look back and recall old established brands that become fashionable (Lacoste, Fred Perry...,) and then fade again. They didn't suddenly become the best products on offer. It was the emotional driver of being fashionable that drove their sales.
The proof is all around us that people buy from their heart so don't try to sell to their head!