Drill down to Customer master for updates

 There are places in Service that allow users to drill down to the customer master.  In most cases, users just view and do nothing.  However, there have been times a user has made changes to the customer that has impacted the entire company.  Service should only have inquiry access to customer master.  But at this time, we are not sure how many ways it can be reached.  Does anyone have the steps or places where the customer master can be accessed from Service?  Thanks for any help.