I think it's useful to know whether an interviewee who has driven into your place of business is serious enough to spend 30 mins learning your platform.
It's fair if the website has useful content. I've been pinged before for not researching the company after their website basically said "we specialize in absolutely everything".
1. how you'd handle customers for various problems? (which seems fair enough).
2. some coding questions (my friend did this in matlab but they wanted him to do it in python).
3. some IQ questions
4. some questions about the platform (which my friend didn't have an idea about as he'd never used top hat before).