Say, you are a Buyer : You can now know your Seller. There are hundreds of fake online sellers and you can avoid ending up a victim to one of those. You can learn from other members and make a wise decision. You can learn about customer service upfront, instead of finding it the hard way!

Say, you are a Seller : You can now, learn about your customer. You can rate your customer based on your experience. Yeah, The customer is always right. We agree. But there are times the customer is unreasonable and often businesses undertake risk and end up with some form of financial loss. You can mitigate risk and catch fraudulent orders upfront. You can post trouble makers' email addresses and fake IPs along with your experience.

 
Say, you are an Observer or just noticed something : You can share what you noticed and your opinion of a particular website or for instance, a transaction on ebay. In a nutshell, you can learn from others' experiences.