Cross selling is a sales tactic that involves offering additional products or services to existing customers. Up selling is a similar tactic, but with the aim of offering a more expensive product. In cross selling, the product does not have to be more expensive, but can be an accessory. For example, a customer buys a mobile phone and the seller offers additional accessories such as a mobile phone case or a memory card. Such cross-selling does not only apply to e-shops, where additional products or services can be displayed at the time of purchase, but also to face-to-face sales, where the seller offers additional products or services directly to the buyer.