How does hikashop handle if the item in cart is already out of stock?

Hi,

It is not be possible as far as I know. Are you able to reproduce the issue ?
However, several things:
- If a product has variants, and that the variant has a stock, the stock of the main product is ignored. So if the user purchased a variant of a product, and that variant has stock, even if the main product itself has no stock, the system will allow for the purchase.
- The stock is checked at the end of the checkout, when the order is created (on top of being checked each time the cart is loaded). However, once the order is created, the stock is not checked anymore as the system considers the order validated. But the payment itself doesn't necessarily happens immediately. If the user chooses bank transfer for example, it's possible that you receive the payment only several days later. Suppose you have a product with a stock of 1 and you've configured HikaShop to decrement the stock when orders are confirmed (after the payment is made). Then, it is possible for users to create several orders with that product as long as none of the orders are paid immediately. So I would recommend checking on this.