Some people never give top marks on surveys. This is not unusual, but typically very limited to just a few customers. Keep in mind, the objective to gathering feedback is not to get a perfect score, but to get genuine feedback so you’re able to make more intelligent decisions for your business.
However, if you find you have majority of customers answering with a Passive response (i.e. answering only "Likely" to recommend, or only "Satisfied"), then you may want to consider having us change your question choices from the 5-Phrase scale to the 11-Point scale.
The 11-Point scale offers customers 2 choices for Promoter and 2 for Passive (i.e. 2 choices out of 11), which maps to a single choice of "Very Likely" (Promoter) or only "Likely" (Passive) in the 5-Phrase scale (i.e. 1 choice out of 5). Hence, using the 11-Point scale gives customers who never give top marks the option to rate you as a 9 (10 being the top) and this is still considered a Promoter.
The general rule of thumb on surveys, is to choose a scale and stick with it. You don't want to flip-flop between scales as it renders your historical comparisons useless. In rare circumstances where a large percentage of your customer responses are Passive, then switching to the 11-Point scale (and then sticking with it), may be the best course of action.
INFO: More information on the NPS can be found here - How to Interpret Net Promoter Score (NPS)