And what makes you trust somebody?
That's a good question... But in order to answer it, you should think about yourself and how you react to other offers online... When it comes to online then I am sure that intrinsically all of us are skeptical in the first place, unless its a known brand such as G, FB, Amazon, Ebay, Coca-cola .... etc - whom have spent billions with building trust with consumers and on many channels from Web, TV, Radio. Newspapers, Magazines etc...
So with the above mentioned exception of known brands - ask yourself - why and who did you buy online from? What was it that made you make that plunge with purchasing?
Chances are that they provided great value straight off the bat... Really helpful tips, advice, helpful articles/videos and perhaps free reports/ebooks... and are fun and engaging when it comes to social media... They understand your pain points, have empathy which demonstrates expertise.... They build trust over time with a proven track record with interacting with you either via email, posted content and interacting on subscriber comments etc... in other words consistency being an important ingredient...
When surfing the web look at others and keep asking yourself this question - Do I trust them and why? ... Over time you'll identify and adopt an approach which will work.... Good luck ;-)