Preventing OS administrator/root account access to data

Hello.
Let's say in a commercial environment where you install the database in a customer's server and their IT people have admin/root access to this server. How can we make sure that they don't get direct access to the database (e.g. like editing pg_hba.conf and setting it to trust). We don't like them messing up with our data and the postgresql configuration. Otherwise, it would be very difficult to support them if any problem arises. Is there a way to disable reading of the pg_hba.conf or maybe preventing the admin/root from modifying configuration files? any suggestions? this applies to both linux and windows.
Thank you.
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Christopher Brian L. Jurado
Primary Software Development Corporation
www.primesoft.ph

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