The customer, instead of making one purchase during the course of a year, makes three purchases. That same customer refers your business to four other people. Your bond is not merely for the length of the transaction but for as long as say, twenty years. And the cost of follow-up is not high because you already have the name of the person. The cost of prospect follow-up is also not high.
Email makes it even lower.
But you can consistently follow up, never giving up and realizing that if you're second in line, you'll get the business when the business that's first in line messes up. And they will foul up. Of course you do. They'll fail to follow up enough. Jay Conrad Levinson is probably the most respected marketer in the world.