Arguably democracy as we know it in its current form is a forced form of democracyn if not a dictatorship, purchases are a more natural form of democracy by voting with your money and purchases, ergo some activities would not be hidden away and science would have a more accurate picture of human behaviour than is currently on display.
On the point of they do not know, humans are creatures of habit, it is possible to know where money is being laundered and its not a single step process.
But a simpler example would be looking at the reCaptcha I'm not a robot process.
So google dont know what these random images are when they present them to people in recaptcha. The user does not know who these images have been presented to previously if at all. Users treating it as a hurdle will click the right images, the malicious user trying to mess up the image recognition will deliberately tick the wrong image. Over time, google gets to find out what images are a bike or plane or traffic lights, helping to train their visual recognition AI models, or at least clean their streetview dataset, they also get to know who are the deliberate malicious users.
So with money going into a supermarket, periodically money is taken from tills and sent off outback for the bank. This is a snapshot of the serial bank notes during a period of time in the supermarket. The checkouts also know what amount of money was handed over. If money is being laundered as cash in a supermarket, or pub, its possible to identify who these people are from cctv, over repeat visits. You see not everyone will be making a monthly food shop, some are just buying lunch so might only hand over £10, someone laundering money will do a monthly shop handing over £200 or £300 pounds.
As these places tend to receive cash and hand out coinage, its possible for the banks to work out the cash trail of money from spending habits. Same goes when money laundering is taking place around an area, like weekend holidays paid with cash. What these money launderers dont know is how many other people from their base area are also on holiday in the same place like a weekend away a few hundred miles away?
There are so many ways to track cash but I dont think most people think about it. The fact people are using cash is a deliberate red flag for a start. Sure some jobs are best done using cash like taxi firms, fast food outlets and pubs, but these are also red flags for scrutiny as well. Arguably its just another form of intellectual surveillance.