A soldier walks on the bank of the river in central Pyongyang, North Korea on April 16, 2017. (Photo by Damir Sagolj/Reuters)

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.

Fans watch during a match between Daria Kasatkina, of Russia, and Coco Gauff during round-robin play on day four of the WTA Finals tennis tournament in Fort Worth, Texas, Thursday, November 3, 2022. (Photo by Ron Jenkins/AP Photo)

Photo taken at the top of the Canton Tower, a landmark in Guangzhou, on August 7, 2022 shows the Pearl River running through downtown of Guangzhou, capital of south China's Guangdong Province. (Photo by Liu Dawei/Xinhua News Agency)

Miniscule larvae carve winding tunnels as they eat through small leaves in a small forest near the town of Velbert in western Germany in July 2022. The hungry green sawfly larvae measure just three millimetres in length and are difficult to spot on the leaves of the beech tree unless up close. (Photo by Christian Brockes/Solent News)

A serviceman of the Carpathian Sich Battalion is seen at his position on a frontline, as Russia's attack on Ukraine continues, near the town of Lyman, Donetsk region, Ukraine on December 8, 2022. (Photo by Viacheslav Ratynskyi/Reuters)

The sun rises behind The Royal Liver Building in Liverpool, Merseyside on Tuesday, January 17, 2023. (Photo by Peter Byrne/PA Images via Getty Images)

MSP Ash Regan and Lexie take part in Holyrood Dog of the Year on June 26, 2023 in Edinburgh, Scotland. At the annual contest, jointly organised by the Kennel Club and Dogs Trust, members of the Scottish Parliament compete with their dogs and Dogs Trust rescue dogs for the title of “Holyrood Dog of the Year”. (Photo by Jeff J. Mitchell/Getty Images)