It must be earned. When you do this, you build confidence. When people receive helpful ideas from you over a period of time, they can't help but trust you. Security Next, you need to help people feel safe in your Web site. You gain something, but you'll turn many away.
People are appropriately hesitant to give out personal information.
Put people at ease. Promise not to sell their address for commercial purposes, and then keep your promise. Because spamming brings immediate new business. But it doesn't build the reputation for courtesy, respect, and customer focus that you need for the long term. People need to feel they can trust you to respect their privacy.