Even with clearly articulated service level agreements (SLA) or metrics that you wish to analyze with an MSP, someone within your organization must own that relationship to ensure: one, the knowledge of what those expectations are, and two, that there are feedback loops when expectations are not being met.
Should my business leverage Managed Service Providers?
Managed service providers can provide third party expertise to help your business grow at the pace you wish to grow, without the cost and risk of hiring employees at the exact time you need them.