Go to admin panel and epesi Store, open Installed modules, CRM - optional components and install Account Manager. This way every Company will be assigned an Account Manager. Then go to Contacts and Companies and adjust Permission Rules accordingly - who can see what. For example Managers can see all records and Salespeople only those where they were assigned as Account Manager.
Besides - in epesi every records contains (never modified) record of who and when created a record. It is easy to see the entire history of the record and verify who was the creator and the owner of that information.
This seems to be a common issue among salespeople. To avoid creating duplicates I suggest to limit view of the record but still make all companies visible to all employees. For example every user will see that there is a company XYZ from ABC town (this information is publicly available anyway) and see who is the responsible person (Account Manager - and you can rename it to), but can not see the phone number, address if you wish, no contacts, notes, activities.
All of this is possible in Record Browser - Permissions.
