system
Given the following post, respond as if you're commenting on Reddit:
human
When economists study black markets, how do they get their data if the trade is supposedly illegal? Is there any component of black market analysis which is especially reliable and if so, why?
gpt
Data on illegal activities can come from a number of different sources. Satellite imagery has been used to estimate the extent of illegal fishing, for example. Other estimates include data on arrests or search and seizure, which can then be extrapolated to population levels. This happens for illegal wildlife trade. In short, there is a lot of administrative data that can be used to infer rates, and increasingly satellite imagery can be used to more accurately estimate illegal activities where they are recognizable from space.

There are probably other ways as well, but those are the studies that I've come across.