Sales copy - as created by "copy writers" - is basically the process of creating a piece of writing that will influence others to buy a particular product or service.
The key thing to realize with the most effective "copy" is that it has almost *nothing* to do with the product. It focuses on WHY the product would need to be purchased, and what the underlying benefit to the user will be.
To do this, copy writers have to basically immerse themselves into what the product was designed to do - not what it "is". This switch - from focusing on the functionality of a system onto the underlying benefits it may bring - is what determines the effectiveness of an "offer" you may want to make to an audience.
How does this work and what does it mean?
Imagine you're writing "copy" for high-end tailoring (suits etc). The suits are great as a "product" - but what you need to realize is that your "job" as a sales person is to "sell" the buyer on the reason *WHY* they'd want a tailored suit in the first place.
The biggest mistake that copy writers make is they will typically try to sell the user on the "quality" of the product (fabric softness etc). Whilst this works well as a validation of a product's offer, it does not really "trigger" the buyer wanting to purchase. To do that, you talk about the way the product will be used - and the effect it will have on the user's life...
Women will never be caught staring. They have peripheral vision which they use to great effect. This, however, does *not* make them immune to the impulse created by the raw of a razor-sharp dresser. Stand out from the crowd with a CUSTOM suit - designed just for you...
This process - of putting a user's core benefit first (and it's typically emotional) - at the core of the offer, is what triggers the initial attraction for a product. This triggering is not by accident - it's as guttural as breathing, and explains why some nonsense products end up being accepted by the market.
The truth is that there's ALWAYS some sort of underlying "breakthrough" that powers successful products. Rather than relying on the product itself, focus on personifying this breakthrough, and you'll eventually start to attract an audience who shares the sentiment. This is then when you start to follow-up with the initial attraction by describing the effectiveness of the product, its quality or some other feature-based ideas.