Before you even begin your search for an IT expert, carefully define your objectives (including specific projects). That way you'll know the skill set you require. Once you've found a list of candidates that possess these skills, ask them to talk about past projects they've successfully completed
When you've found the proper candidate, ask him or her to provide you with an expectation of costs before work on the project begins. Then devise a timeline and definition of deliverables that you expect them to complete. Finally, ask the consultant to sign nondisclosure and noncompete agreements to prevent them from leaking or reselling your project to your competitors.
For more on hiring, be sure to read How to Hire an IT Expert.