Here is a short post on doing right by your customers. It’s not rocket science but it’s surprising how bad most companies treat their customers.
This post is focused on payments and cancelations, but I think there are other related issues.
For example, popups and notifications might add 5 or 10% more subscribers to a website, but what percentage are you annoying that you’ll never know about? 50%, 60%? I immediately close sites with multiple popups and notifications. If they don’t care about my experience on their website, I’m not going to signup for anything.