I would ask them 3 key questions to highlight their genuine knowledge over and above certifications. These are the three questions I ask every new SM in our organisation.
1. What came first, Agile or Scrum?
90% of respondents will say Agile. They believe that Agile is a "thing", a framework, a methodology or an approach. They believe Scrum and Kanban and others were a result of Agile.
That is incorrect. Most frameworks and tactics existed long before the Agile values were enshrined in the Agile Manifesto. If they cannot answer this correctly (and you should be able to as well) then it is not a definite blocker but it is a yellow flag.
It normally means I have to coach them to see frameworks as a big bag of tools; a buffet of mental models. Once they get that they can select most appropriate micro or macro tool to unlock delivery regardless of the official guide.
2. If I understand Systems Thinking can I understand Scrum, if so, why?
The basic answer is that almost every iterative framework can trace it's genesis back to Japan and Taichi Ohno in some form or another.
Which means that arguing about Lean Six Sigma versus Scrum is like arguing about the New Testament versus the Old. They are all the same Genesis and all broadly seek to achieve the same aim; continual delivery of business value through the reduction of inefficiency. Some focus more on root cause analysis but in general if you subscribe to one framework you are really subscribing to them all. I have heard actual Scrum Masters refer to Kanban as dumb, inferior etc and tout Scrum as the one true way. That is the enemy of Agile thinking.
3. Can you give me genuine examples of how the Scrum Values translate into every day life in a Feature Team
You are looking for specifics. An easy way to identify an academic Scrum Master is to probe for how they work daily at the tactical level. An example might be
I RESPECT the Scrum ceremony by not bringing my laptops and typing during Sprint Planning;
If my mind, you should not only seek to hire a Scrum Master. You are should hire a person tasked with building great engineering teams, strong iterative ethos and frequent deliveries of value.
Scrum is one way of doing that and you want to make sure that any Scrum Master you hire shares that same mindset. A Scrum zealot will sink your organisation as fast as a 10,000 line MSP plan.
Amateur Scrum Teams argue about tactics. Professionals study integration.