Possibility to purchase goods only once per user?

Question

PHP

Good afternoon, tell me how to implement the ability to purchase goods only once for a user, preferably on opencart, but other engines are also interesting to know. There will be no registration, just a new user selects a product and from this computer, for example, will no longer be able to buy.

Answer 1

Possibility to purchase goods only once per user?

You decide: will he be a GUEST or a REGISTERED USER?
For a guest - no options!

Answer 2

When buying, give the user a cookie with the product ID, and then check if he has the right cookie and then prevent him from buying the product with a specific ID, if there is a cookie.