No magic bullet . Outsourcing is not a magic bullet that relieves you of all associated work. To ensure a successful project, communicating early and often is critical. The challenge, though, is finding the right vendor. To help ensure the right fit, there are a number of areas to explore with the consultants.
Relevant experience is clearly the first area to investigate.
Any firm you work with should have previous experience in performing what you want accomplished. More specifically, the actual staff that will be working on your project should have the experience that you need. Otherwise, you risk finding yourself paying for their training. When it comes to staffing, it pays to get into the details. Of course you have a deadline, but life happens.