Swinburne University student Tara Siri, 21, said she was walking with friends down Spring Street last month when a "monk" approached them bowing his head and smiling, before pushing a plastic hologram picture of Buddha into her friend's hand and asking for cash.

"First she was like 'Oh, I don't have any money' but then he kept smiling and handing her the picture. She got out her wallet and handed out $2, but he wanted more. He really put the peer pressure on," Miss Siri said.

She also noticed the clothes underneath the smiling assassin's robes deviated from the traditional wear.

"He had ... tracksuit pants and sneakers on," Miss Siri said.

"They're taking advantage of people's first impressions. The reputation of Buddhist monks is really positive, you'd have no reason to doubt someone who would come and do that."

Greg Campbell, 46, sells The Big Issue on the corner of Exhibition and Bourke streets and has noticed gangs of monks harassing pedestrians towards Elizabeth and Swanston streets.

It's an area where charity collectors are hard to avoid and far from being annoyed about money that would otherwise go to reputable organisations like his own, Mr Campbell said he just feels sorry for the people who donate to them.

"It embarrasses people, they feel they have to give money," he said.

Buddhist Council spokeswoman Susan Wirawan, who has also been approached, said the organisation has received numerous complaints in the past six months.

"Monks do go out on the road and looks for alms, but usually they accept food. They don't go out soliciting (money)," Ms Wirawan said.

"They're not good practicing Buddhists. If they were they would understand the teaching of Buddha is quite against that; using your Buddhism to make profit."

A Consumer Affairs spokeswoman said they had received a number of complaints in the past six months and if people had doubts about a charity's legitimacy they should donate directly to organisations, rather than to people collecting on the street.