What is considered a “user”? Our customers don’t create accounts to checkout, but we need each person to only be allowed to order one product once. My concern with the IP address tracking is that a lot of our customers will be in one office. Doesn’t that mean they’ll have the same IP?
A user is either a person with an account or if they are a guest, they are tracked by IP. In your case, if they are in the same office, the plugin will consider them as the same user. It is not possible to track users in any other way.
You could use the option of asking customers to create an account on checkout.