Know Your Product. Believe in Your Product and sell with Enthusiasm
These are the fundamental selling truths. If you don't know your product, people will resent your efforts to sell it, if you don't believe in it, no amount of personality and technique will cover that fact; if you can't sell with enthusiasm the lack of it will be infectious.
Nothing turns off a potential customer quicker than a salesman's lack of familiarity with his products. Have you ever walked into a department store, asked a clerk how a particular gadget or appliance worked, and then stood by while he fiddled with the knobs and wondered out loud why they don't make things simple anymore? Even if he finally gets it to work, by that time your interest has diminished and you are not likely to make the purchase.
Knowing your product also means understanding the idea behind its projection, how it is perceived – the relationship between it and what someone wants to buy. How will it help the customer? What problem is it solving? What is its promise?
An understanding of these intangible features is at least as important as knowing a product's mechanical features. Yet precisely because they are intangible, and may even vary from customer to customer, they are more prone to being misinterpreted and misunderstood.
Knowing your product also means understanding the image it is projecting. I believe all products project an image of some sort. It may be a positive one, which you want to promote, or a negative one, which you need to overcome.
The home computer industry, for instance, really didn't take off until it solved its image problem. Here was the device that saved time and simplified all sorts of tasks, yet it looked complicated and difficult to use. Until it was made to seem ``friendlier'', less forbidding, sales lagged.