To protect your investment, get a written contract. Some of the specific issues that should be addressed in the consulting contract or letter of agreement are:
Most consultants bill on a time and material basis. Therefore, to protect the interest of both you and the consultant, set out a reasonable work plan with a not-to-exceed (NTE) cost. A work plan is like your blueprint, it maps out exactly what the consultant has contracted to perform, with timelines and estimated costs at defined stages. Use the proposal received from the consultant as a guide when drawing up your work plan. In some instances the work plan may vary due to the nature of the project, so a series of possible scenarios and costs should be built around best case, worst case, and most likely scenarios.