This is private and confidential information. And can vary market to market.
Books maintained in company are 2 types. They usually have a separate book for taxes. And a separate book to keep margins, under invoicing, and all such costs.
For such practice 2 invoices are generated 1 for customs and 1 for the customer.
International clients know how things work for Pakistan.
For example, since I am from textile il give you certain examples.
In India their is a rebate on importing brand new machine. Indians buy old machines, refurbish them and import them as brand new.
If a item in pakistan has an ITP value of lesser value. People would declare lesser value send extra money by illegal means to save taxes.
If anything costs 5.5 per kilo and ITP value is 4.
People would declare it 4 pay taxes on 4 while actual worth of goods without taxes is 5.5 per kilo.
If you declare 5.5 you have to pay taxes on 5.5
