Here is a link to a provocative article, which I recommend you read, especially if you’ve implemented the Net Promotor Score (NPS) in your client survey systems: “Net Promoter Score Considered Harmful (and What UX Professionals Can Do About It)”.
Jared Spool argues the widely used client satisfaction score at best is useless, and more troubling, could provide inaccurate assessments of client satisfaction.
Customer experience is the sum total of all the interactions our customers have with our products, sites, employees, and the brand. Every sequence of interactions will differ for every customer.
People who believe in NPS believe in something that doesn?t actually do what they want. NPS scores are the equivalent of a daily horoscope. There?s no science here, just faith.
Note that Spool is not arguing against surveying clients for satisfaction; he is just advocating for different questions and more natural metrics, that would truly express the gradations of client satisfaction — and asking them when the are appropriate.
Here are some alternatives:

How delighted or frustrated were you today?

Have we been helpful today?

Did we make you happy?
I don?t think it matters, assuming what you?re truly interested in is the next question or some variation:

What would?ve made it better?
The follow-up question is where the value is. You can ask it a multitude of ways. What?s important is you to listen to your customer.
These questions don’t provide a hard and fast “number” that you can use in your management Powerpoint or spreadsheets, but they would give you insights into whether you are delivering the service you promise.
As for me, for the time being, I’m continuing to use the NPS question within the context of certain client surveys — notably our “new client” survey for Ontario Construction News.? But it is just one question, and (much more important to me) is the follow-up:? “What is the one thing we can do to make you happier.”? This question has exposed some gaps and problems in our services, invoicing processes, and client communications. I certainly (especially based on Spool’s article) would NOT base my assessment of success on the actual NPS score number, though — even if it is truly satisfactory.