Before you try to convince someone else, make sure that you are already convinced about whatever it is that you are trying to sell. It can be a product, a service or an idea. The first sale is always to yourself. Once you have bought into it, you have understood why it is good and how it can be of benefit, only then do you share it with others. If you skip that very important step, you risk your chances of success. People can sense if you are only selling something for the sake of making a sale or that if you really believe in it. You might not be able to actually afford it, that is not an issue. Although it would help if you are also a satisfied consumer yourself. The main important thing to focus on is the genuine enthusiasm that you convey to others about it. That can often times make or break the sale.