- What is my break-even ROAS, and what do you need from me to calculate it?
- What would you check first in my account, and why that first?
- Who will be in the account, and how many others do they run this week?
- Who owns the account and who pays Google?
- What is the notice period?
- When did you last tell a client to stop spending?
- What would you refuse to work on?
- Can I speak to a client directly?
None of these require them to reveal anything proprietary. All of them are hard to answer well without actually doing the work.