Very commonly we have feature requests for fields that only one customer wants. This, at best, clutters the application's code. Often when we look in their database a few months after adding the fields, we can see that they are not actually even using the extra fields. Also, it's quite an old application so adding a single field requires multiple code changes, changing reports, and making sure that it doesn't affect other customers who do not need to see the field.
How can we make sure that a customer actually needs these feature requests?
How do we politely say "you don't really need that"?
Currently we are beginning to charge for certain feature requests. (Previously, feature requests were free usually) Is there anything else we can do?