Do product previews actually help sell digital items

Let me describe the situation first of all. I run a small e-shop. Niche - self-educution, self-improvement, personal development etc. Products are imported from different sources: PLR, Sellvia Mall, IDPLR. I have a problem of good number of visiting while sales are not so good. Im wondering if the products are not being sold when people can't really check the full content beforehand.
My questions:

• Do you think showing a few sample pages or screenshots makes a difference?
• Should I focus on while making a product description? What is the most important?
• Can showing too much of the content actually put potential buyers off?