This keynote from Meet Magento New York 2014 is "Persuasive E-Commerce" by Guido Jansen. Online merchants have a big problem because online conversion rates are very low versus offline. Offline - 20-25% conversion rate; online is 2-10% conversion rate.
Online sales don't have the same level of personalization and sensory input as offline stores.
Automatic thoughts and actions drive much of our purchasing behavior. These are called heuristics in psychology, and they can lead to cognitive biases and prejudice.
Always be testing.
Social proof is a powerful force. Try things like in the past month X customers bought this product. This works well for socially acceptable products, but not for socially undesirable products.
Authority, liking and scarcity are other forces that persuade us to purchase.
There is no average customer - there are large individual differences.