This concept can be applied to any type of products to services: to be trusted you must first give value for free. This requires patience.
Always. Be. Helping.
New to a community? Volunteer. Offer to help. Share your expertise. Don’t have the expertise? Lend your time instead.
Listen and ask and raise your hand. Build your rapport. Build your karma. Build your credibility over time.
Then, and only then, have you earned the right to ask for something in return.
You need to build the trust before you can cash in on it.
(Aside: When you’re given an opportunity to step up, don’t squander it by overstepping.)