Starting Up: What is a customer, anyway?

A customer is someone who pays you.

Not somebody who used to pay you, but stopped.*

Not somebody you've talked to a whole bunch and it's looking positive, but who hasn't paid you yet.

Not somebody who's thinking about paying you.

Not someone who might pay you, if they knew about you.

Not an imaginary persona you think would definitely pay you, were they to exist.

A prospect becomes a customer when cash changes hands, and ceases to be a customer once cash stops changing hands.

* This rule doesn't really apply to one-off products; when you sell one-off products, somebody who bought one product exists in a sort of quantum state, they are a customer, having paid once for a pay-once product; but they are also a prospect and could become a customer again.