Consultants in testing

I like consultant testing staff but a few things that I have found that can be issues are:

1. Make sure that the experience matches what has been stated in CVs.
2. Consultants should be managed closely to ensure they are conforming with any corporate practices.
3. Often people within a company will assume specific business knowledge not possessed by an external consultant. Assistance should be provided to fill in this knowledge gap.
4. Consultants cost more than internal staff so should be sought with a specific purpose in mind.