In the UK in WW2, we had true shortages of food and many materials that came by ship due to the Nazi U-boats.
The government implemented a pervasive ration system, books, stickers, coupons etc. Stores would get, say 100 pounds of butter. Only people with a ration book pulled out stickers(good for one pound of butter) could get them. The system was granular and butter might need 10, sugar 6, potatoes 2 etc. There were also meat coupons. Rich people bought black market goods made from real goods. You could take 100 pounds of butter and create 105-110 packages of butter with printed copies of waxed paper butter wrappers. If they looked OK = it works. The grocer could make more $$ on those 5-10 created pounds of butter than they made on the remaining 90-95 pounds. After the war, shortages endured for 1-2 years, very granular. After he was demobbed, my father was a glazier = repaired windows. If a bomb was dropped, it might flatten 1 house, but it would break the glass in 200-300 homes. After the war = huge glass shortage = rationed. Glaziers were allowed 5% breakage and cutting allowance. My Dad would order only 1 size, for one common type. If a customer wanted a smaller size = he refused, said no glass. He was able to make more on that 5% than on all the rest of the crate of glass. Money was tracked. In the UK then the largest currency was the 5 pound note.(with 1 pound and ten shillings the others = all else = coins) He had 15 suitcases of 5 pound notes. This was called 'fiddling'
So price controls = 2 parallel markets. A true market and a black market for richer people. This was policed, but not closely and with care black marketers escaped. I hear there is a black market in rubles, about the same as the Rasbucknik", of which one was worth nothing, and a large quantity was worth even less, due to the trouble of lugging them around, as was found in lower slobbovia
https://en.wikipedia.org/wiki/Lower_Slobbovia?