You win customers by focusing on their needs. You keep them the same way.
Focusing a great deal of attention on buyers during the buying process and then relegating that same buyer to poor postsale service means customers are far more likely to leave. This can lead to a churn cycle in which companies add more sales resources to replace the customers who abandoned them, and around and around it goes.
You keep customers happy, not by doing something different from how you won them in the first place, but by doing exactly the same things that won them in the first place. Shifting strategy doesn’t work.