A wi-fi rating is feedback to let the person you play or trade with and other people what your experience was like with that person. To leave feedback, click on the person's name, select view profile, then you should see a tab on the top of their page that says "Wi-fi Rating". Click on that and then you should see an option on that page that says "Submit feedback for (username)" Click on that and fill out the form. Usually, people just say the experience was positive and leave a short comment like "Thank you for (whatever that person did for you)." If you were scammed by someone, then you would leave a negative rating and explain what that person did.