Feedback question.

I'm curious regarding some of the feedbacks for my A'gon sales. I've sold a few pieces equipment to members who have then sent positive feedbacks stating that I was a purchaser of their equipment. I even got a similar feedback from a member whom I've never dealt with. Is this done to underhandedly give themselves positive feedbacks or just a mistake? Has any other member had a similar experience?
I'm not using my member name to avoid bad vibes for myself and those who have sent feedbacks.