A good vendor will provide their product or service as the customer desires, and otherwise mind his or her own business.
Like the bartender that keeps selling drinks to someone that is falling down drunk. Or, you take your car to the mechanic and tell him you need a timing chain, he finds out all you need is a tune-up, but he puts on a timing chain anyway. Or, a breeder sells a Border Collie to a frail old woman that lives alone in a small apartment.
These are NOT good vendors.