Well, adding a single component to an already existing system is also a service offered by a hi-fi-retailer. In that case, the consumer would likely be the instigator, the retailer providing guidance and advice and potentially a loaner piece for the client/customer to take home to audition in his system. The problem with that is that many consumers have no such local retailer that provides that kind of service.
But now we are back to the issue and premise of this posting! It is a fortunate consumer who has a relationship with a hi-fi-retailer possessing enough integrity to resist a short-term sale in the interest of a maintaining a long-term relationship with a repeat customer.