I've just posted a response to something similar on another question, not sure if this is you?

I'll keep this answer a little more concise:

- You must know what platforms they have used and what platforms they haven't

- You must know the sectors they have worked in, and those they haven't

- You must know their high-level achievements and how the metrics they use to measure success

- You must know the lower, more tactical achievements they have made and how they have come up with tactcal ideas and deployed them

- You must know if they can write compelling ad copy for your industry

- You must know the budgets they have experience in working with

- You must know the aspects of PPC they want to improve and learn

- You must know whether they keep up to date with changes in PPC and if so, can they demonstrate how?

- You must know the ad campaigns they admire and why

- You must know what they consider to be the biggest opportunities and risks in PPC in the next year

- You must explain your goals for PPC with them, how you came to the decision you needed to invest in PPC and get some thoughts from them about how they would approach working with you, at least in the first couple of months.

Good luck!