Justice David Mossop heard the second day of the trial of Chang-Kee Song, who has pleaded not guilty to a charge each of trafficking in a controlled substance, being heroin, and money laundering.

Defence barrister James Stewart had previously argued Mr Song was not a heroin dealer, but one of a group of users pooling their finances to buy the substance in bulk to save money.

But a witness, under questioning from prosecutor Katie McCann, said she had bought heroin from Mr Song, who she knew as "John", on a number of occasions and had also cleaned his house in return for heroin when she could not pay.

That witness said she believed Mr Song was a heroin user, not a dealer, but had asked him why he had started asking for money from her for drugs, as they were "friends".

But, under questioning from Mr Stewart, she said she did not expect to obtain heroin for free from Mr Song, and she had not asked him how much he was buying the illicit substance for.

She said Mr Song said he had to ask for the money to help his mother come to Australia and she had accepted that explanation.

But Mr Stewart argued that that conversation had "never happened", and she may have misinterpreted Mr Song talking about saving money for his mother, rather than using money gained from heroin.

A series of ACT Policing criminal investigations officers also took the stand, detailing a surveillance operation and subsequent search of Mr Song's Phillip home in June last year, on suspicion he was involved in heroin dealing.

A series of phone calls were played in court, some of which included conversations between Mr Song and various callers the prosecution alleged discussed arranging heroin deals.

But Mr Stewart argued those conversations did not necessarily indicate arrangements for drug deals at those times, but could instead be "orders" placed by other people, as part of a joint bulk purchase of heroin shared among them at a later date.

Officers said the search of Mr Song's home led to the discovery of almost $400,000 in cash as well as 4.362 grams of heroin, just shy of the five gram threshold for trafficking, among other drug paraphernalia.

Mr Song was arrested and searched during the raid, which revealed he had $1035 and some small bags of heroin in one of two pairs of pants he was wearing at the time, and officers also found some $19,130 lying on the kitchen table.

After Mr Song's arrest, one officer said, he had told them that "what you are looking for is on the kitchen table" and that he was "a heroin user, but I buy in bulk".

Police told the court they searched the rest of Mr Song's home, ultimately finding a digital safe wrapped in a sheet in a storage area under the house at the back of the garage, inside which was $377,905 in cash, a count later found.

The trial continues tomorrow.