How many Uber clients do you build cabinets for?
If he doesn't build cabinets for uber rich guys, then I bet he builds cabinets for guys who do work for uber rich guys. Those uber rich guys pay them cash for their labor commodity, which in turn is used to purchase Karl's labor commodity.
I work for an insanely rich guy. His net worth was about $35mil this year. He provides me a great living in return for my labor commodity. (Along with 5000 other employees - his company started with like 20, back in 1996 btw)
My Dad was a construction worker - built the DC metro, then sold life insurance door to door during the doldrums of the 70's recession after he graduated from a fine school with a great liberal arts degree. He ended up becoming the executive vice president of the largest custom home builder in America - by selling homes to mostly uber-rich people. He employed thousands of workers to get this done, and in the process, provided his family a great living.
Liberals hate the term "trickle down" economics - as well they should. The mainstream media has led you to believe that all of the rich people take their dollar beels and stuff them under their mattresses, or shred them into confetti for some extravagant display of their wealth at a friend's dinner party. I don't know for sure what this view of wealth and economics is based on, but I have a good feeling that its motivated by jealousy.