People avoid buying books because of a lack of time. In this case, they get it 45 seconds after asking. I've had 24,000 hits on the site in the past four weeks, and a huge number have clicked to buy it. The same principles can be applied to other products. Give people an incentive to contact you and start a dialogue, then upsell with the permission they give you.
Every business has permission opportunities with customers.
When you buy a burger, for example, you're asked if you want fries. Or you're in a store and the clerk asks if you would be interested in buying something on sale. You've already given them permission to sell you something, and that can be leveraged. It's more cost-effective to increase sales to existing customers than to run ads to find new ones, yet most businesses don't seem to appreciate the value of what they have. The business owner hasn't calculated the lifetime value of the customer.