Have you ever bought something nice? I bet the salesman was quite sure of himself that the item he wanted to sell you was the right one at the right price. Even more, he wanted you to know you were getting a great deal. Was it true? Maybe. Maybe not.
What you do know to be true is how much he wanted you to believe that he believed you were getting a great item at a great price. I don't know if you ended up buying it or not but would you have been as interested if the salesman himself was not? There are plenty of salesmen who can certainly lie and pretend, and may very well make good sales. However, the best salesmen truly believe what they're telling you. The salesman's belief in it is what makes it all the sweeter, as far as he's concerned, he can't get the sale unless you believe that he believes what he's saying. What better way to help that along than for him to actually believe his own words? Anyone can look at the specifications, observe the conditions, and make a logical judgment on whether the price on the sticker matches the value of the product. So what's the use of salesmen?
The reason is, most people can't make such big decisions to do big things unless someone talks them into it. The same is true in dating. In a sense, you are the product and you are the salesman for yourself. I am not saying to hang a price tag around your neck and start soliciting your body on a street corner, but effectively you are selling yourself, your personality, your positive traits, your values. You are selling this to the opposite sex so they will "buy" what you got. So think about this for a minute. If you didn't believe in your own product, how do you expect to get any sales?
You truly need to value yourself and see yourself as a great deal. You need to convince yourself until you can't believe anything other than 'you are a great deal'. When you can do that, you will be a lot closer to what you want than ever before. What is there to be afraid off? What is holding you back? If you don't see yourself as a "prize catch" or "best deal ever", how will others see it either? I am convinced you can do this.
Bar advice. The saleman's belief must be self thought. Now reflect on what you've been lacking and change the sales pitch of your life.