One of my biggest frustrations with some of my clients is that they are constantly on the look-out for the next digital agency; being acutely aware of the flaws of their current provider.
The issue is that they are woefully unaware of their own shortcomings when it comes to managing the agency. Often the agency isn't the problem, the problem is the way the client works with the agency...
Every time you think the problem is 'out there', that very thought is the problem
- Stephen Covey
Agencies need access to people outside of digital.
Agencies need deeper data access
Agencies need time
No agency can deliver three year growth in a one year contract ... and why would they try? Be realistic and build for the long-term. The digital agency must have enough time to work with your various stakeholders to build long term value, don't expect any huge incremental improvement inside of a six-month probation - so don't even write it into the contract.
If you trust the agency at the start of their contract with you, then you should consider that they are trustworthy and you should give them sufficient runway to learn about your business and customers before achieving stellar campaign performances.