Adding a Sales-Driven Feature
Question: "What is the guideline to support adding a sales-driven feature?"
According to the Blackblot PMTK Methodology™, you should add a one-off feature, .e.g a feature that only one customer had requested, only if that new feature augments your product's Unique Selling Proposition (USP).
The USP describes the distinct and compelling value of the product, which sets the product apart from other competing products. So the USP is something in the product that is both a competitive differentiator while simultaneously providing value to the customer.
Being unique and valuable, the USP is also justification to command a higher price for your product. Adding any one-off feature that strengthens the USP will not dilute the product's feature set with divergent and minimally used features.