The duties of waiting staff can be tedious and challenging but are vital to the success of the restaurant. Such duties include the following: preparing a section of tables before guests sit down (e.g., changing the tablecloth, putting out new utensils, cleaning chairs, etc.); offering cocktails, specialty drinks, wine, beer, or other beverages; recommending food options; requesting the chef to make changes in how food is prepared; pre-clearing the tables; and serving food and beverages to customers. In some higher-end restaurants, servers have a good knowledge of the wine list and can recommend food–wine pairings. At more expensive restaurants, servers memorize the ingredients of the dishes and the manner in which the food is prepared; for example, if the menu lists marinated beef, the customer might ask what the beef is marinated in, for how long, and what cut of beef is used in the dish. Silver service staff are specially trained to serve at banquets or high-end restaurants. These servers follow specific rules and service guidelines, which makes this a skilled job. They generally wear black and white with a long, white apron (extending from the waist to the ankles). At expensive restaurants, waiting staff also keep blacklists of rude customers.