Great thread.
I would definitely get an idea of the CPA's client base. As a client, would you be their largest, smallest, or somewhere in the middle? If you're not sure where to begin, ask what the firm's gross billings are for the year, how many professional staff they have, what their clients average gross revenue is, and what they anticipate (range wise) it would cost for the service(s) you are requesting.
Your goal is to grow your business, do they know how to help you do that?
It's important to know how well versed the firm is relative to your investment. Are you a single investor with a single property and need some light bookkeeping assistance? Or do you have multiple K-1's with cross collateralized debt, layers of flow-through ownership, inter-company loans, inside and outside basis, side management companies, employee leasing companies, 401(k) plans, estate tax plans, etc etc.
Also there's more to consider than just the tax preparation. Do you need financial statements? Do they need to be reviewed or audited? Or will a full disclosure compilation suffice? How about other services such as business valuations, debt negotiation and credit restructuring?
You should walk away from the meeting with ideas for your business plan or accounting strategy that you didn't have before.
If your CPA/EA isn't comfortable stepping into a quazi CFO role during the course of the conversation, could they really be a trusted business adviser? Would you want this person speaking to your lenders or partners on your behalf?
Your relationship should be symbiotic; they should provide more value than simply filling a compliance need.