“We don’t act when we don’t trust you”
We are a suspicious species. Therefore trust is a very important factor when it comes to online persuasion. Corritore et. al (2003) define online trust as follows: “an attitude of confident expectation in an online situation of risk that one’s vulnerabilities will not be exploited”.

So if we’re confident that our vulnerabilities will not be exploited, we’re more likely to act.
Scientific Review:
Beldad, The Young & Steehouder (2010) did a meta-analysis and identified the following key elements that increase online trust:

Perceived ease of use of the website
When a website is easy to use