Scrum Master should understand the domain or product on which team is working
I have been observing in one of the Scrum teams that they tried introducing a new Scrum Master who is unaware of the technology and product on which the team is working. Scrum Master contributes only by asking team members to put comments on their user stories, estimate them and sending mails and calendar invites. After 3 months of waiting (where I assumed that Scrum Master will be able to develop product understanding and contribute to team), I see team is still not able to get even a single benefit from Scrum Master. Due to this, even some team members estimate their stories in a way where they can put estimates according to their wish as they never get any question raised. I feel Scrum Master role can be taken up by any member in the team whether developer or tester but not by any outsider who just supports tickets redirecting for the product.