Won't UDEMY find out about this and shut down your account? Sharing this is against their terms of service:
You will not reproduce, distribute, publicly display, publicly perform, communicate to the public, create derivative works from or otherwise use and exploit any Company Content, the Products or Courses or Submitted Content except as permitted by these Terms or the relevant Instructor as applicable;
https://www.udemy.com/terms/So what happens if we give you a large order order and pay for it, and then your method of getting these accounts gets patched and your account banned?
Because of this big risk, I would say that if I bought from you, we must use an escrow where the funds will only get released upon receipt of all the courses as promised. If any less, the escrow should only release the payment of those courses that are received and then refund the rest back to the buyer