Many People Would Like to Sell and Buy on EBay

Many people would like to sell and buy on eBay but are unsure how much to charge or pay. A company called Keen.com has set up a directory of specialists to whom you can address questions. Users can see the ratings given to each specialist by previous users before they contact that specialist. Which service component does Keen.com use to help its customers evaluate its service quality?

A) empathy
B) assurance
C) tangibles
D) flexibility