What it boils down to: the buyer needs reassurances and clarifications before buying. Three simple ways to do that:
- Explain why you're asking for the customer's details, don't just ask for them.
- Tell the customer what will happen after they give you their email, don't make them guess.
- Present signs of trust (e.g. verisign or other lock symbols) to reassure the user that their details (particularly payment details) won't be stolen.
... it is crucial to address key concerns (conscious and subconscious ones) at the right stage in the decision process.
In other words, every page until you've made the sale is part of your sales process, and should sell your product in whatever way is most appropriate for this stage of the interaction.