Is it permissible for a salesperson to sell on credit at his personal responsibility and realize a profit margin in exchange for this risk, knowing that the company prohibits selling on credit except at his responsibility and implicitly encourages this?

The salesperson is an agent for the company, and he must abide by its instructions. If the company contradicts his order to sell products on credit, he bears the responsibility and is considered a guarantor, because an agent is not permitted to sell on credit (deferred payment) without explicit permission from the principal. However, if the representatives add a profit margin for themselves in exchange for the risk, there is no harm in that if it is with the explicit permission of the company. Otherwise, the agent must return the surplus to the company.