In Default Interface Accounts, there is no purchaser column to set as default

Customer requests to set purchaser as default to different user in the system.

1. Go to File > Modules

2. Tick User Default Settings. Additional module incurs extra charges. Save & Close.

3. Create a user at Defaults > Security System User. Set the roles.

4. Go to Default > User Default Settings. Select the User created just now.

This example uses User Default Settings. You can use another similar method which is User Default Role Settings. 
Refer to below link on how to set the user roles.
 https://support.qne.com.my/support/solutions/articles/81000389123-how-to-create-user-and-user-roles-video- 

5. Select default purchaser for this user at Purchaser

6. Untick “Allow to select to other purchaser” 

so that this user can only select the default purchaser.

7. Tick “Allow to select to other purchaser” 

so that this user can select other purchasers also instead of just the default purchaser.

so that cannot see transactions and reports by other purchasers

so that can see transactions and reports by other purchasers

10. Tick “Compulsory Select Purchaser”

so that user cannot save without key in purchaser.