How should I rate a Professional and why?

You should give feedback on your Professionals performance when your business is concluded. This allows you to register your level of satisfaction, and it helps the Professional deliver you excellent service. It also helps to give other Businesses (or you in a future dealing) an idea of how good a professional is to work with. The better the Professionals rating, the higher the perceived credibility. This is not a guarantee, but one of many ways of qualify and select the right Professional for the job. No one is perfect. 5 stars does not mean the person was perfect. It should indicate to everyone who views that Professionals profile, that they are highly recommended to other business clients.
Please be honest and fair in your ratings. Discuss with your Professional to avoid misunderstanding