Xue here from the Shopify team to help you out.
With your specific request, this won't be natively available with our Shopify platform as it appears to be very unique to your business set up. Not to worry, a solution like this can be found in an app. Check out Order Limits, they appear to be offering the service you're looking for when limiting products to one-per-customer.
Let us know how it goes, otherwise, if you'd like to discuss this further feel free to reach out to our Support Team at any time.
All the best,
Xue | Shopify Guru
In this case, does the app have the ability to remember the previous person who bought the course and won't let the person buy the product again?
Say I am selling online courses and the person buys my course, then he/she attempts to buy again the second time.
Can the app recognize this and reject the order for the same course?