Descriptions of the deals are often emailed to customers when the deal goes live, sometimes with creative or humorous descriptions. The practice of sending these emails has been criticized by e-mail marketing professionals and users. However, evidence suggests this aggressive strategy is effective at generating sales. Some sites allow members to receive an e-mail either daily or weekly or to be notified of all current offers. Customers purchase the deal on the deal-of-the-day website, rather than directly from the retailer. The websites then retain the customer data, rather than the retailer.