The Black Market
Simply put, so long as there exists more than one person on the Earth, there will also exist the potential for a scarcity of any given commodity. Regardless of how fairly resources are distributed, any time there are n two year olds and n-1 marbles, you're gonna have a problem. Someone is not going to have a marble. Someone is going to find a way to get one.
In previous eras, black markets thrived because goods that were scarce could always be had, for a price. The seller was able to profit from the sale of his goods and convert them into either other valuable scarce commodities, or into currency which he could use in the official market. In our world, the only way to obtain goods on the black market is by exchanging other scarce commodities, and of course services.
The "oldest profession", prostitution, has the potential to play a key role in the black market today, as sex is one commodity that is always in demand with or without the existence of money. For this reason, our society punishes prostitutes and their customers severely. Both are mandatorily sent to the Penal Colony for a minimum of one year, if they survive. The reputation of the Penal Colony is in itself a significant deterrent to crime. One might consider the punishment cruel and inappropriate for the crime, but the social implications of an illegal sex trade are tantamount. A sex-based black market could undermine all that we have worked to accomplish in the world today. This threat was realized by earlier authors such as H G Wells, who painted a picture of a world where sex was purely mechanical and lacked all passion what so ever. We have chosen to keep passion in our lives, and instead punish harshly those who abuse this pleasure.
It is natural that one citizen will from time to time have access to a scarce item that another citizen might want, and they may wish to make a deal. "I'll trade you those two lobsters you were able to get today for the ten yards of fine silk fabric I have that you wanted". This type of interaction is not only commonplace, but also quite legal. The one citizen was entitled to two lobsters and rightfully obtained them. She may now have to wait some time to get her hands on two lobsters again. Both scarce items are being used, not wasted, and everyone is happy. It is not until there is intentional diversion of quantities of goods that a true black market exists. When a case of fine wine is diverted from the stock room of the store and sold in exchange for a case of diverted lobsters or for sex, then a black market exists.
Even so, one might think that citizens would hoard scarce goods every chance they get, so that they may bargain with others for the uncertainty of what they may need some day in the future. "Wow, they have fine knit wool sweaters! I am going to take home a half dozen of those, and I'm going stop off and pickup two bottles of that rare Scotch I saw earlier today, just in case I need it to trade sometime." Throughout their schooling, our citizens are trained in civics and respect for the fair appropriation of goods and services. Simple hoarding is not punished, but large scale hoarding, which is clearly defined by law, is punishable.