1. The photos of the members are casual, taken by friends or family
2. The site offers affordable monthly prices rather than per-message charges
3. If you search for reviews of the site on the internet, you find many more good reviews than bad
4. The site takes your security seriously. It should provide general advice on how to be cautious of internet scams as well as specific examples of scammers, should have all pages secured with SSL, and should be certified PCI compliant.
5. It is easy to reach customer service by phone, and they are not pushy to make a sale