Who should write the items for your customer survey? Your customers.
Two questions to ask to ensure you understand what matters to your customers:
1. How do you rate the service out of ten?
And then for anyone who rated it less than 9:
2. What would we have needed to do for you to rate it ten?
And you learn what matters to your customers.
You could also ask those who rated you 9 or 10: what was it about the service that made you rate it that way?