FYI... those tabs only display to the Ad Owner and Staff
The Transactions Tab only displays for the Ad Owner and Staff and only for Ad Type's For Sale, For Rent and Service.
In order for the Ad Owner to see the "Transactions" tab, they must have the permission "Add / manage transaction on own ads"
The Items Tab only displays for the Ad Owner and Staff and only for Ad Type's For Sale, For Rent and Service.
In order for the Ad Owner to see the "Items" tab, they must have the permission "Add / manage items on own ads (multi-item ads)"
Simply unsetting those 2 permissions in ALL of your User Groups will take care of it for Ad Owners.
As for Staff members, they can always see those as they need to be able to access any LEGACY transactions and or items that might be associated with the Classified Ad.
Template customization is not covered by support, however, if you look in the template
xa_cas_ad_wrapper_macros
, you will find a MACRO named "tabs". Inside that macro is template code for each tab. You can comment out or remove the template code for the "items" tab and "transactions" tab without breaking anything (again, not supported, so you need to know what you are doing).
Hope that helps