I'm by no means a legal authority, but I believe they are requiring this because the corporation is a seperate entity from the individual that may own all of it's stock. Small corporations are typically a guise to shelter a business person from liability, or from taking personal losses due to suits against their business activity. Appraisers are not allowed to shelter their personal assets from suits for professional misdeeds.
You may want to ask your attorney if it would be more prudent to incorporate your property rental business - and have your appraisal corporation rent office space, equipment, car, residence for CEO as part of the benefit package, etc, etc, from the rental corporation.
Properly orchestrated, incorporating can be an excellent tax saver. Improperly orchestrated, it can expose you to double taxation, and not limit you liability losses in the least. This is not a do-it-yourself job. It IS a job for a dedicated and experienced professional attorney, specializing in corporate and tax laws.
Good luck. Pass on any pearls of wisdom that you find in your research.

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