The difference isn’t about difficulty, but about what you’re asked to do with your knowledge.
Let’s take the Daily Scrum as an example. I’ll ask you a question for each level, with sample answers, to see if you’re ready to take the exam.
For PSM 1, the question will be: what is the timebox for the Daily Scrum? I’ll give you three answers.
- As long as it takes?
- One hour for a one-month Sprint?
- 15 minutes max per day?
The correct answer was 15 minutes maximum.
For PSM 2, the Daily Scrum always starts late, which cuts into the time available. What do you do?
- I do nothing, it’s up to the Developers to organize themselves.
- I start on time, too bad for the latecomers.
- I bring the question to the Developers and ask them what they think about it.
The correct answer was to bring the question to the Developers so they can explain what the problem is and choose the solution that best fits the team, by improving themselves. Whether it’s changing the Sprint start time or trying to arrive earlier, the Developers are best placed to make that decision.
For PSM 3, the question will be: a Developer refuses to come to the Daily Scrum. He says it’s pointless. What do you do?
PSM 3 is the only exam where there’s no predefined answer. You have to type your answer and justify why you’re making that kind of decision.
So here’s what I propose: write in the comments what you would have answered to this question, and I’ll tell you what I think.
In summary, PSM levels 1 through 3 all test your knowledge of Scrum and the Scrum Master role, but at different levels. One asks you to recite, the other asks you to coach and support teams.
Sources: https://www.scrum.org/professional-scrum-certifications/professional-scrum-master-assessments