We learn by comparing our behavior to others.
What options do you offer people on your site to compare their behavior to other visitors? Show them how others interact with your website and/or products through twitter/ facebook/ comments/ a forum. Show what the most popular products or searches are ('people who looked at eventually bought product X'). You can also highlight or reward people who demonstrate positive interactions with your site ('customer of the month' or a list with 'most active commenters'). Further reading on Mimicry at the Wheel of Persuasion.
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Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.