People take part in a Halloween street party at Lan Kwai Fong on October 31, 2016 in Hong Kong. Halloween, a contraction of All Hallows' Evening, falls on the day before All Saints' Day on November 1, a holiday when Christians remember their deceased loved ones. (Photo by Lam Yik Fei/Getty Images)

Crowds look on as the super moon rises behind the Fremantle War Memorial at Monument Hill on November 14, 2016 in Fremantle, Australia. A super moon occurs when a full moon passes closes to earth than usual, with the November 14th moon expected to be closer than it has been in over 70 years. (Photo by Paul Kane/Getty Images)

Everyone wants to get something for nothing - whether it's a lucky upgrade that means you can turn left when you get on a plane instead or heading off into the economy seats, or even getting a few extra features thrown in for free when you buy a new car.

As some of the sharpest businesses around, no-one understands this quite as well as casinos and that's why they all have a system that they call comps. It's short for "complimentary offers" and these are special treats specially designed to reward you for your loyalty to the casino in question. They're basically bonuses.

Wang Zhengqing, a 74 year old pneumoconiosis patient, smokes his pipe at Yangjia Hospital in Wuyi County, Zhejiang Province, China October 19, 2015. Former miner Wang was diagnosed with the disease, which is caused by dust inhalation, when he was 24 and has lived at Yangjia Hospital for ten years. (Photo by Damir Sagolj/Reuters)

Mave Grace, 11, who had part of her arm chopped off by militiamen when they attacked the village of Tchee, stands with her sister Racahele-Ngabausi, aged two, in an Internally Displaced Camp in Bunia, Ituri province, eastern Democratic Republic of Congo, April 12, 2018. (Photo by Goran Tomasevic/Reuters)

Vehicles are burning as thousands of people take to the streets during the May Day demonstrations on May 1, 2018 in Paris, France. This month celebrates the 50th anniversary of May 68 when France seen millions of students and striking workers, come onto the streets in demonstrations that changed the country. (Photo by Jeff J. Mitchell/Getty Images)

A David Cameron look-alike poses with a polar bear model outside the Houses of Parliament as part of a Greenpeace protest on May 13, 2011 in London, England. The environmental charity Greenpeace arranged the protest to highlight the first anniversary of David Cameron’s speech when he pledged to make his new government the greenest ever. In April 2006 Mr Cameron traveled by huskie-drawn sledge when he visited the island of Svalbard in Norway to witness the effects of climate change. (Photo by Oli Scarff/Getty Images)

Yanna Xian, 24, and her boyfriend Mitch Brown, 27, were swimming while on a boat tour off Honolulu, Hawaii last year, when a curious two-week-old humpback approached them. (Photo by South West News Service)