Ask HN: How do you make sure your customers are happy?

I would love to get some insight from all you business owners out there as to how you make sure your customers are happy and that they stay with your service.

- Do you use any software? - How do you collect feedback? - What do you do if one of your customers wants to stop using your service?

If you were to use a product that would help you make sure your customer satisfaction stays up, and your customers stay with you, what would you look for and where would you go?

Thanks, HN.