As an employee of a company, it's important to obtain a receipt when purchasing anything on the company's behalf. If you negotiate an additional discount and wish to keep it as your personal incentive, you may ask the store owner to increase the bill amount, which they may refuse to do. If another employee is later tasked with buying the same product, they may be informed by the store owner of the earlier transaction or notice a lower charge on their receipt, potentially causing issues with transparency and trust within the company