When we make decisions, we rely too heavily (or anchor) on one trait or piece of information. Especially when the situation is unknown, we tend to appraise information based on a single known anchor from which we then make relative adjustments (this is also known as the Focusing effect).
Provide your visitors with anchors to influence their decision making (eg. the original price of the product) or present an attribute/ number as being more important than it really is (eg. the number of megapixels on a DSLR camera). Even completely irrelevant numbers can influence the buyer if relevancy is suggested in some way.