I would hope Udemy can start doinng something about what I have decided are currency traders - they buy the course, wait a day or two, and refund. They are usually gobbledegook email addresses which makes me groan when I see them - I don't count them as earnings even for a day.
They buy in $ at one rate, then refund when the exchange rate improves even a little. If they do that enough with bots across Udemy - bingo. Wish I had thought of it.
And, of course, if they are human, they have lifetime access they can on-sell with their nonsense email ID.
JP