" The reality is that only one or two aspects of your offering have real value to your customers. The rest are merely nice to have. If you doubt that, the next time a customer asks for something special, attach a price to it. If they pay, they truly value what they've requested. If they refuse to pay, the request was merely an attempt to see how good a deal they could get. Buyers will not be denied what they truly desire; they will find the money if it's important enough to them. "

― , Pricing for Profit: How to Command Higher Prices for Your Products and Services