The one service is worth another

People seems to be forgotten that the world is not progressing without effort for each other.
What does it mean?
Let's take an example: if a seller has received money from the buyer for a product, then the transaction is finished??? No! From time to time, this seller will give the customer an extra attention: giving some interesting prospects, more advice, a little gift from the company, after-sale service...
Why is it useful? To come back another time, of course!
The whole Marketing is to please the customers, like (s)he is to be considered as a long-lasting friend! It's a booby-trap, don't you think? Business is business. There will be no love (pleasure) involved because it is fake! It's why after you buy something you like, this 'something' is making you unhappy... It is only bought with money and not with a heart (with others). Mislead by 'lovely' commercials.
The whole thing is: if you do something more than selling a product, to add a worthfull / trustfull / not-expressive-in-money-valued gesture, which the client hasn't even expected, then (s)he will be happy about his (her) product and will come back for another time.
Welcome everybody!