How to cover the materials costs from users

how can we hide items’ average and total cost from our sales points? I mean users

Simply by clicking edit columns and deselecting average and total cost, see screenshot.

but the user can simply clicking edit columns and return the selections

That is a case of internal discipline within your business. I am actually amazed about quite some posts including this one where those in charge can not trust their employees. If that is the case they should not have access to the accounting application.

Many posts relate, including some of my own to the fact that Manager is not a suitable Point of Sales system and that you are advised to use a separate one (search the forum). Manager is excellent to help with accounting.