The Black Index's Planet Strange Gold subdivision controlled half of the Galactic Black Market's hires and funds in the Ancient Star Desert. Controlling this place meant that half of the black market's movements were being monitored.
In the main control room, the Third Indexer ordered the operators to open up the firewall and let Han Xiao inject his data needle, planting a ton of surveillance programs while looking at the documents behind recent anonymous hires in the black market.
The Black Index's internal database had records of the true identities of some employers, most obtained through investigation. As the intermediate guarantor, the reward of the hire would go through the Black Index before going to the mercenary. Therefore, following the source of the funds, it was not difficult to find the identities of the anonymous employers.