Just how do we define 'customer'?
One of the most difficult things in data-driven marketing is getting agreement on what some commonly used terms actually mean. It is somewhat unfortunate that databases and computers are totally ignorant -- they simply reflect what we tell them to hold and do, so we have to be explicit in our instructions.
The answer to the above question is the proverbial "It depends." Only somewhat tongue-in-cheek I've argued the following funnel:
Sales -- any warm body
Marketing -- anyone with a need
Legal -- anyone we're allowed to talk to
Finance -- anyone who can issue a purchase order
Accounting -- anyone who owes us money
Similar funnels can be created for terms like 'revenue' -- contracted vs. booked vs. collected.
Rightfully or wrongly data-driven marketing requires us to sharpen our definitions to the point that computers and databases give us the right answers.