You don't know why your customers buy from you!
Do you know why your customers buy from you?
The fact is that you don't!
And whatever you are thinking of is probably wrong.
I know that for sure because if you did you could expand your business at will and you can't do that!  Just look at most of the franchises.  They understand why the customers buy from them so they can put their stores everywhere around the whole world!
You can't.
Let me give you marketing scenario that will show you that it is not the product that people buy. 
Once upon a time in 1987, a smart marketing manager had the job of selling Red Porsche Turbos in Silicon Valley.
He found two types of people that had money to buy.  One was the marketing guy for the chip companies.  The other, much much richer, was the engineer for the chip companies.
He understood that the marketing guy was a people person so he put an ad in Playboy with a Porsche Turbo at the beach, the owner standing in front, a beautiful girl hanging on to him and a bunch of friends smiling at him.  He was the hero.
The marketing guy saw the ad and bought a Red Porsche Turbo with Chrome wheels.
The marketing guy, being a smart guy also decided to go after the richer group, the engineer for the chip company. 
He put an ad in the technical journal that the engineer reads.  It showed a cut off of the combustion chamber of the engine showing the swirl pattern of the fuel going into the the combustion chamber that resulted in more horsepower and better mileage.  The engineer, duly impressed, bought a Red Porsche Turbo with Chrome wheels.
One day at a stop light in silicon valley, the marketing guy pulled up to the red light in his Red Porsche Turbo with Chrome wheels and stopped. 
About a second later the engineer pulled up to the stop light in his Red Porsche Turbo with Chrome wheels, an identical car.
The marketing guy looked over at the engineer and thought, well there's an engineer who as usual is still wearing his 10 year old dirty jeans.  The engineer looked over at the marketing guy and thought, there's a marketing guy with no brains at all so he needs to dress up and lie for a living. (If you've ever lived in Silicon Valley you know what I mean :-) ).
Well the light turns green and both Turbos take off.
The marketing guy is thinking.... I'm so hot I've got a date with Mary Sue and she'll love my car and love me!
The engineer is thinking... Just listen to that airflow! This machine is a marvel!
Now I ask you again.
What are you selling?
You don't know!
In the case of the Porsche Turbo two totally different concepts are being sold!  It's the same item but viewed totally differently.
Do you now understand why you don't know why your customers are buying? 
Unless you are very focused in your marketing you really don't know.  Your customer just buys from you because your competitor doesn't have good marketing to take him away from you.
But, inevitably, sooner or later, a smart competitor will have good marketing and take your customers away from you just as my knowledge has allowed my clients to TAKE SALES FROM THE COMPETITION.