The one week course, undertaken by 25 officers, comes with a civil case currently before the courts over an alleged wrongful arrest.
In a separate case the government paid an undisclosed amount of money to settle with a man who was also wrongfully arrested at the Fugalei market by armed officers.
Police Commissioner Fuiavailili Egon Keil said the training was a reminder for all officers how to carry out their duties.
"We can't just arrest people for the sake of arresting.
"In the past, it seems like the practice was reversed where you make the arrest then you do the investigations later on," he said.
"No, you make the investigation first, then you make the arrest if there is enough evidence."
Fuiavailili said police needed to follow the law themselves.
He said police were working closely with the Attorney-General's office on any issues.
The Fiji Police Force partnered with Samoa's Ministry of Police to carry out the training which was opened by the British High Commissioner, David Ward.
Mr Ward said his government had been able to contribute funding to make the training possible as one of the first projects since the opening of the office in Samoa this year.
The training was designed not just for police to understand rights of detained and arrested people but to prevent torture in custody.
Fiji's Deputy Police Commissioner Itendra Nair, who was one of the training facilitators, said police in his country were pleased to share their experience of implementing the United Nations Convention against Torture with their Samoan counterparts.