避免电子商务场景中的竞争条件

My client has a ecommerce website that sells electronics, and there has been situations where a product is sold more times than they have in their inventory. This is because if two users buy a product at the same time when there is only one product left in stock, one session does not finish registering the product as sold out before the other session starts(so it continues as normal, thinking there is one left) even though there is a check in place at the beginning of the process. This would obviously cost money (chargeback fees, refunds, etc.) and inconvenience for the consumers. My client has a ecommerce website that sells el