What a great question: What's a customer worth?
That is a title of a blog post from Seth Godin.
"A customer at the local supermarket or at the corner Fedex Print shop might spend $10,000 or even $25,000 over the course of a few years. That's why marketers are so willing to spend so much time and money on coupons, promos and ads getting people to start doing business with us."
In a Citi bank prezo from 8x8, there is a slide of Customer Lifetime Economics. These are some important numbers for valuations.
LVC determines how much you can spend to acquire a customer profitably. It should also be a guide to your entire staff that this isn't just a customer but your salary. Adjust policy and attitude accordingly.