A vigilante who films alleged paedophiles in elaborate sting operations is at the centre of a major court test, as a judge considers whether one of his videos can be used to help prosecute an accused child sex offender.

Sydney YouTuber Amir Hawatt, who posts under the pseudonym FaZe Nighthawk, became an internet sensation by filming elaborate sting operations targeting suspected child predators.

While his videos have led to two convictions, his latest sting has sparked a legal battle in the case against Sydney man Jeremy Howell, 42, who is accused of procuring a child for sex.

Howell, 42, appeared in one of Mr Hawatt's YouTube videos about nine months ago after the vigilante confronted him at his workplace.

During the confrontation, Howell admitted to sending 'naughty photos and comments' to someone he believed was a 14-year-old girl.

The messages had actually been sent to Mr Hawatt, who was posing online as an underage teenager.

After speaking with Howell, Mr Hawatt contacted police, who later arrested the 42-year-old.

During a local court hearing earlier this week, the judge heard arguments over whether the video, relied on by police, is admissible as evidence or whether it unlawfully breaches Howell's privacy.

If the video is ruled inadmissible, police will not be able to use it in their case against him.

Mr Hawatt also gave evidence this week, telling the court: 'I just decided to pivot into something, that I'm able to produce content and at the same time do something good for society.'

The case is due to continue later this year.

NSW Sexual Crimes Squad Acting Superintendent Rachel Fawcett told Channel 7 police were supportive of 'the notion' of citizens helping to catch child sex predators.

'We support the notion of catching predators online and working with the community to do that,' she said.

But she warned Mr Hawatt's actions may not be admissible in court.

'It may not hold up at all,' she warned.

It is understood Mr Hawatt is exposing himself to the risk of both criminal and civil proceedings, including allegations of harassment, assault, stalking, illegal recording and defamation.