The completed Request view form on the support site shows a field for entering a rating of the quality of Request fulfillment.
The client can specify the rating value and enter a comment on the rating. Inside the support project this information is shown in the "Client rating" (Feedback) and "Rating comment" (FeedbackText) fields.
The client can also leave a rating by following the link from the Request completion email, which also offers to rate the quality of the work.
For a systematic analysis of your support team's work quality, you can create a "Satisfaction" metric. Go to the "Metrics" module and create a custom metric of type "COUNT/AVG", then fill in the fields as follows:
The current metric value can be added to the control panel. In the "Charts" section you can track how the value of any metric changes over time.