Real illegal market functions in one of the Moscow subway stations: drugs, forged documents (especially passports of the Russian Federation), diploma papers, school leaving certificates, driving licences and other services are easily rendered here.
It is very difficult to shoot the very moment of the deal as the market infrastructure includes observers and courriers, a man with a camera gets noticed very fast.
These people have their own system of signs.
Police doesn't want to notice the "market".
The Moscow subway was chosen for the " forgery office" not randomly, despite being overcrowded it is a safe place where people don't pay attention to anyone except themselves and their own hurries.