Although the general public thinks of underground forums as a place where scams and suspicious dealings are rampant, the opposite is usually true: the threat actors who inhabit these sites often consider their reputation a major asset.
Many of the individuals and groups in underground forums go to great lengths to ensure that transactions go through without a hitch, implementing a system of checks and balances that include vetting, the use of escrow and deposits, as well as arbitrage for handling any problems. Underground forums also have strictly enforced rules that prescribe the use of polite and ethical behavior — certainly with a hint of irony when considering the unethical purpose of many of these websites.
This level of trust and ethics is especially important considering these threat actors have the ability and qualifications to attack each other.
Source: Trend Micro