Celeste Renard, owner of Sensual Linens Shop, was preparing checks for payment of the current month's purchase invoices when she realized that there were two invoices from Passionate Linens Company, each for the purchase of 100 red, heart-imprinted king size linen sets. Alexander thinks that Passionate Linens Company must have billed Sensual Linens Shop twice for the same shipment because she knows the shop would not have needed two orders for 100 red linen sets within a month.

How can Renard determine whether Passionate Linens Company billed Sensual Linens Shop in error or whether Sensual Linens Shop placed two identical orders for red, heart-imprinted linen sets?

If two orders were placed, how can Renard prevent duplicate purchases from happening in the future?