A man presents a self-made robot that local media reported is able to carry a person, in Heihe, Heilongjiang province, China, April 5, 2017. (Photo by Reuters/China Daily)

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.

Girls take a selfie at the haze shrouded Batanghari River bridge in Jambi, Indonesia Sumatra island, September 14, 2015. Indonesian islands are blanketed in the so-called “haze”, caused by slash-and-burn clearances on the islands of Sumatra and Borneo, which makes thousands sick, delays flights and pushes air quality to unhealthy levels in neighboring Singapore and Malaysia. (Photo by Reuters/Beawiharta)

Breeder of baby goat Mohammad Hasan Narejo and a child show ears of 2-month-old female baby goat named Simbi in Karachi, Pakistan on June 07, 2023. Simbi has the world's longest ears which are 55 cm. (Photo by Sabir Mazhar/Anadolu Agency via Getty Images)

This picture taken on June 3, 2023 shows wild elephants eating rubbish mixed with plastic waste at a dump in the eastern district of Ampara. (Photo by Ishara S. Kodikara/AFP Photo)

Lauren Metzler, founder of Sydney Mermaids, prepares for a swim at Manly Cove Beach in Sydney, Australia, Thursday, May 26, 2022. There is a strong need, especially after COVID-related lockdowns, to simply play and enjoy creativity, Metzler says. (Photo by Mark Baker/AP Photo)

Coco Gauff celebrates during her victory over Aryna Sabalenka of Russia in the women's final of US Open at the USTA Billie Jean King National Tennis Center on September 09, 2023 in New York City. (Photo by Shannon Stapleton/Reuters)

Japan fans pose for a photo outside the ground ahead of the Rugby World Cup 2023, Pool D match at the Stade De Nice, France on Sunday, September 17, 2023. (Photo by Mike Egerton/PA Images via Getty Images)