When is "the extra mile" a bridge too far?

I've read some books by Dr Paddi Lund, an Australian dentist whose surgery has:

• A locked front door
• No advertising
• No new patients unless Paddi invites one of his existing customers to make a referral

One of Paddi's recommendations to other business owners is to educate your customers BEFORE they buy from you. He believes that "customers are just waiting to be led".

But that has to be tempered with "going the extra mile" for your customers. If the product can be modified just a little bit, without deviating from the business's core aims, to make a customer a Raving Fan rather than a Satisfied Customer (hat tip to Ken Blanchard and Sheldon Bowles) isn't that a good thing?

Because, in these hard times, Satisfied Customers will go elsewhere even more readily than usual. Raving Fans will stay.