Here is some good advice on how to manage a consultant from the Voice of Small Business:
Define the problem or issue to be addressed, especially mindful of its scope and boundaries.
Investigate the expertise of the potential consultant. Talk with previous clients, look into completed projects, and assess the education and experience of the consulting staff.
Know the consultant’s fees and how they are determined (hourly rates, fixed fee or other arrangements).
Establish the responsibility for expenses, determining in advance who pays for what and what expenses are included (for example: travel, lodging, food, etc.)
Determine a payment schedule.
Determine what documentation is required of the consultant and the frequency of reporting.
Specify limits on the scope of service or length of engagement.
Before signing a contract, define objectives, set standards for evaluating progress and identify deliverables (reports, systems, etc.).
Identify reporting relationships.
Establish the means for early termination of contract by either party should this become necessary.
And, the wisest advice of all:
Trust is essential to a successful consulting relationship.