If your organization is willing to hand over all administration of the services to the vendor, do you trust your vendor enough let them take the reins? It is really convenient and cost-effective to use the vendor's expertise for remote monitoring or management, but you really need a team that understands what your organization requires.
Traditionally, organizations had to choose between full control and low TCO. On-premises deployments offer complete control. You are in charge of your own destiny. However, as outlined earlier, on-premises do not necessarily provide low TCO. Conversely, SAAS-based deployments provide organizations with low TCO but erode control. Most cloud solutions abstract away the lower layers of the stack: the operating system, patching, etc. That's a good thing. But they also hide other important configuration and policy controls as well as detailed analysis into logs and reports. That's a bad thing.
We all know that no two organizations are the same. Every organization needs the ability to customize its configuration and requires complete control over the infrastructure. Ask your vendors if they are able to deliver cost savings and provide you with the control over the cloud-based infrastructure. In short, seek those vendors that can give you complete control and low TCO.
5. Customer support
Another area where organizations often compromise when moving to the cloud is customer support. Vendors cannot just "bolt on" a customer support team and expect current support staff to understand cloud computing and SAAS issues overnight. The quality of customer support becomes a huge differentiator between different cloud-based solution providers. Support is essential to maintaining customer satisfaction and data security, especially when things go wrong.