Hi,
No no, I would like to limit each product to 1 per user. And maximum 4 different products per user. Both conditions lifetime. For example:
We have blueberries, lemons, bananas, tomatoes, and lettuces. Every user can by only one each and only 4 in total. So when one user buys one lemon, one banana and one tomato in one transaction, he only can buy or one lettuce or one blueberry next time. And thats all. After this second transaction, he cannot buy any product.