When you set up a coupon code, you can specify how many times it can be used per customer (via the "Per User Limit" field). However, how does CartThrob keep track of this? I assume by member ID, if the user is logged in. But what if they're not logged in? Is it by IP address, by the billing/shipping info they enter for their order, or some other method?
Looking at the code, CartThrob can only use this feature for logged-in members. It cannot track coupon code usage by guests.