Typically, most reviews online are given when the user is unhappy. They take to the Internet to complain. It's always been a struggle to get users to give positive feedback. Not just here on our site, but all over the Internet.
I think that it's fairly common for hams to ask the other party to come to the Feedback Forum and leave a positive review, if they are happy with the product and service. I would not be bashful in shooting an email to some of your previous buyers, and ask if they'd do that for you. I know that this is common because I often get emails from people saying "I bought a piece of equipment from ___ and now he's asking me to leave positive feedback, can you help me get logged in" or similar. Many folks have difficulty grasping the concept of needing to sign up as a new user to post feedback, since the QTH Classifieds does not require any type of login. It is what it is.
73 - Scott KA9FOX