David, there's always an element of chance when you're picking out a consultant, but in general you can hedge your bets by going in right off the bat--before the first phone conversation--having a nailed-down list of what the business goals you want to achieve are, what resources you're able to devote to it and what kind of time frame you're willing to allocate to the project. Having all of that isn't going to ensure a successful relationship, but not having it, and expecting the consultant to hash it out for you, is going to ensure that it will be unsuccessful.
Some great consultants that we highly recommend are 180 systems and 3B Research and Consulting
The most important thing is to find a consultant that is unbiased and really looking out for you and not their wallet. It can be hard to find but there are many great consultants out there too!