Vendors selling vegetables wait for customers under a flyover in the early morning in Ahmedabad, India on February 1, 2017. (Photo by Amit Dave/Reuters)

In this photo taken Saturday, September 23, 2017, a mouse is cooked on a fire after being caught in a cornfield in Chidza, Masvingo Province, Zimbabwe. Considered a delicacy, the field mice are hunted in cornfields where they have grown plump on the grains, grass and wild fruits. (Photo by Tsvangirayi Mukwazhi/AP Photo)

A fisherman carries a silver carp during a traditional fish haul at the Horusicky pond near the town of Veseli nad Luznici, Czech Republic, Tuesday, October 24, 2017. Each autumn, Czech fishermen get to serious business of a century-long tradition of catching carp for Christmas markets. Southern Bohemia, where the Horusicky pond is located, with its elaborate network of ponds is at the center of the local carp universe. (Photo by Petr David Josek/AP Photo)

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.

The first autonomous and electric shuttle of PostAuto Schweiz in the old village of Sion, Switzerland, June 2016. (Photo by Ruben Sprich/Reuters)

“Grit and Glamour”, a retrospective of the late British photographer Elsbeth Juda, who fled Nazi occupation and came to England in 1933, is at the Jewish Museum, in London, until July 1, 2018. Here: Shelagh Wilson, Copacabana beach, Rio de Janeiro, 1951. (Photo by Elsbeth Juda Archive/Victoria and Albert Museum)

Young artists perform at the presentation of clowns in a hall of the Arts Palace during the first clown festival in Belarus in Bobruisk, some 150 km from Minsk, Belarus, 01 April 2018. About 60 clowns from Belarus and Russia gathered to entertain spectators. For 1 day Bobruisk became a capital of Jokes and Humour. Theaters of clownery, mime-theaters, individual performers of humorous genre, stilts and hospital clowns performed on a stage of the Palace of Arts. (Photo by Tatyana Zenkovich/EPA/EFE)

The Leshan Giant Buddha, a 71-metre tall stone statue, is carved out of a cliff face in the southern part of Sichuan province in China. (Photo by Suchet Suwanmongkol/500px)