If your agency's operations are standardized and there are products available, it is worthwhile to evaluate the vertical market option. The primary value of using a consultant is to create high-level custom solutions. Because the requirements are more sophisticated, the costs can be extreme. The benefits of this approach can likewise be extreme - a custom application that is completely integrated with every agency activity. Using the consultative process requires good specifications and a major commitment of staff to the project.
Specifications keep the scope of the project under control, and staff keep the project focused.
The single biggest complaint with consultant-created applications is runaway costs. This is almost always due to scope-creep, where the specifications for the application are increased after the project starts, either through being added on the fly or as the result of poorly defined specifications being clarified at the hourly rate of the consultant. One or more staff assigned as liaisons to the consultant is an important safeguard in this area. Staff who have become familiar with the consultants can facilitate change orders or other enhancements to the scope of work, and help both management and the consultants understand priorities and costs. Good consultants welcome this level of involvement because it helps them do a better job.