This 2014 series Shanghai Tian Wa saw Chinese photographer Liu Tao train his lens on two distinct districts in Shanghai. Here: “Shanghai Tian Wai №26, 2014”. (Photo by Liu Tao/The Guardian)

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.

North Korean leader Kim Jong Un, his wife Ri Sol Ju and Song Tao, head of the International Department of Communist Party of China (CPC) Central Committee, applaud with ballet dancers in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang April 17, 2018. (Photo by Reuters/KCNA)

TV host/blogger Louise Roe attends The Weinstein Company's Academy Awards viewing and after party in partnership with Grey Goose at TAO Los Angeles at TAO Hollywood on February 26, 2017 in Los Angeles, California. (Photo by Rachel Murray/Getty Images for The Weinstein Company)

A hot air balloon competition called “Grudziadzkie Zawody Balonowe” is held in Lisie Katy, central-northern Poland, 14 May 2021. The compe​tition is held for the eighteenth time. (Photo by Tytus Zmijewski/EPA/EFE)

Tao Xiangli gets out of his homemade submarine after operating it in a lake on the outskirts of Beijing September 3, 2009. Amateur inventor Tao, 34, made a fully functional submarine, which has a periscope, depth control tanks, electric motors, manometer, and two propellers, from old oil barrels and tools which he bought at a second-hand market. He took 2 years to invent and test the submarine which costs 30,000 yuan ($4,385). (Photo by Christina Hu/Reuters)

(L-R) Playmates Summer Altice, Monica Sims and Heather Rae Young attend the Playboy party with TAO at Spire Nightclub on February 4, 2017 in Houston, Texas. (Photo by Christopher Polk/Getty Images for Playboy)

(L-R) Playmates Monica Sims, Heather Rae Young and Hiromi Oshima attend the Playboy party with TAO at Spire Nightclub on February 4, 2017 in Houston, Texas. (Photo by Christopher Polk/Getty Images for Playboy)