For Zhang, building trust with suspects is both the most crucial and most challenging part of the job. He said one must truly blend in — speak their language, know the street names for various drugs, and stay informed about market trends, price changes, and supply routes.

"If you don't have that knowledge, they'll start to doubt you — and you'll be shut out from the most important information," he explained.

The challenges of undercover work go far beyond technical skills. Zhang emphasized that officers must possess both mental fortitude and emotional intelligence.

In one particularly complex case that stretched over a month, Zhang was subjected to a series of "tests" by the suspects. They offered him drugs, alcohol, and even illicit services to verify his credibility.

By calmly deflecting and offering believable excuses, Zhang managed to win their trust without compromising his integrity. The effort ultimately led to the seizure of 20 kilograms of illegal drugs.

"These situations require an undercover officer to find the right balance," he said. "You can't break their trust, but you must also uphold your principles."

Patience, he added, is essential. "Many cases aren't resolved overnight; it's a long process of probing, negotiating, pushing, and pulling," Zhang said.