It mainly revolves around the facts that 1) VAT is deductible for companies in certain cases 2) Companies are responsible for collecting the VAT for products they sell and submitting the collected money to the government. These things mean that auditors (and in some cases officials) must be able to verify that VAT has been collected, paid and deducted correctly. Therefore it is important to have receipts which clearly show who sold, who purchased, what was purchased, what was the price and how large portion of price was VAT.