Are selling or upselling?
Upselling is one of those fancy-sounding terms that refers to persuading your customers to engage on a level beyond simply buying a single product or service from you. It could include bringing in external advisers and services into a professional business and introducing them to areas that have a direct impact on their business. It could involve widening your product range with essential or useful add-ons, exactly like what you come across when shopping.
The important thing to remember is that it has to be meaningful and not simply plonked there with little hope of succeeding but instead diluting the value of what your core service is.