Mount Sinabung volcano erupts, as seen from Tiga Pancur village, Karo Regency in Indonesia's North Sumatra province October 8, 2014. (Photo by Y. T. Haryono/Reuters)

In this Thursday, May 25, 2017 photo, Donte, a musician who only gave his first name, straightens out dollar bills on his first day in a brand new Chewbacca costume purchased from eBay for $441, in the Hollywood section of Los Angeles. Donte said he replaced the old one because he wasn't making any money with it. (Photo by Jae C. Hong/AP Photo)

Shortlist, open competition, lifestyle. Healing Vibes – the hot springs of Bagno Vignoni in Italy flow out at a temperature of about 49°C. They were appreciated by the Romans for their healing powers, and have been used as therapeutic treatments since the 12th century, under Emperor Federico II. (Photo by Stefano Butturini/Sony World Photography Awards)

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.

Lady Gaga performs on ABC's “Good Morning America” at Rumsey Playfield, Central Park on May 27, 2011 in New York, United States. (Photo by Andrew H. Walker/Getty Images)

BMX biker and event compere Ben Manuel warms up for the annual Hub Festival May 20, 2011 in Liverpool, England. This weekend's annual hub festival is an urban mix of art, music and action sports staged at Otterspool Promenade and attracts the top BMX, Skateboarders, artists and musical talent from across the UK. (Photo by Christopher Furlong/Getty Images)

A model wears an Apache costume in the kids carnival during The 13th Jember Fashion Carnival 2014 on August 21, 2014 in Jember, Indonesia. The 13th Jember Fashion Carnival (JFC) 2014 theme is “Triangle, Dynamic in Harmony” and consists of ten parades which include Mahabharata, Tambora, Phoenix, Pine Forest, Apache, Borobudur, Flying Kite, Wild Deers, Stalagmite, and Chemistry. This street carnival is claimed to be one of the biggest in the world and comprises more than 850 performers parading along 3.6 km road used as the catwalk. (Photo by Robertus Pudyanto/Getty Images)

Paramilitary policemen take part in a training in Chaohu, Anhui province, China December 28, 2015. (Photo by Reuters/China Daily)