Even cigarettes today, subject to artificially high prices in some northern states, are traded on black markets. Taxes are used in this case as a limited control on a market and create a limited black market. Cigarettes are either purchased legally in states with lower taxes or hijacked from trucks and sold illegally in the higher priced markets.
In the Soviet Union, if you had 10 calves one year, and you could report that you had 8, you were taking a risk, but it had high potential benefits. The 8 you reported were going to be taken by the collective and you were going to get some pittance for each one. The other two, raised in secrecy and butchered, could be sold for a high markup, either in cash or goods. This meat was delivered to customers who knew someone and had the resources to pay. It could also be applied to a few bushels of wheat, potatoes, or any farm product. The diverted products were the only ones that returned a profit free of the fixed prices and central control.
Don't think so? The lovely single payer system in Canada already has the problem. Faced with wait time approaching 10 years for gastric bypass surgery, people are paying $10,000 to be moved up the list. Some doctors only show up for surgeries and births if they get a direct payment in cash. More than 50,000 Canadians gave up, traveled abroad, and paid out of pocket for surgeries in 2014.
I picked Canada as an example but the former Soviet system, Cuba, Great Britain's NHS, even North Korea, have the same issues. Government limits result in shortages, denial of service, long wait times, and those thing inevitably give rise to black markets.
And to close, a quote from The Guardian, in a June 2014 article where they proudly report that the British healthcare system has been been ranked as best in the world. You can't make this stuff up, folks.
The NHS has been declared the best healthcare system by an international panel of experts who rated its care superior to countries which spend far more on health. The same study also castigated healthcare provision in the US as the worst of the 11 countries it looked at....The only serious black mark against the NHS was its poor record on keeping people alive. On a composite "healthy lives" score, which includes deaths among infants and patients who would have survived had they received timely and effective healthcare, the UK came 10th.