Well, it isn’t really all that uncommon for illegal stuff such as this to be publicly advertised. What they usually do is to phrase things in a nice innocuous code, and count on word of mouth through the community of their clients to pass on what the actual meaning of things is. So they might say something such as, “SMOKED HADDOCK: $5,000 PER TON”, and any potential clients would see that and know that it really means, “CHEAP YUGOSLAVIAN ASSAULT RIFLES: $5,000 PER CRATE”.
It only gets awkward when some innocent unsuspecting fellow shows up actually wanting to buy several tons of smoked haddock, or when the police notice that a certain notorious criminal has suddenly developed a rather spectacular appetite for smoked haddock from a particular company.