One of the best bits of advice I ever had was: "it is x times easier to sell to an existing customer than it is to find a new one". (I think x was 5 but I can't remember lol).
This is a huge point and can't be stressed enough. It goes back before Search to your business model. I am of the opinion that ANY business model that doesn't include a way to get customers to come back and buy again is just leaving big piles of money on the table for someone else to pick up. If your product or service is only ever going to be purchased once, then find more or different products. Because otherwise, your shelf life is limited, and some other commodity pusher will always eventually beat you out.