A prolific fraudster who poses as a fisherman is believed to be returning to Waikato.

The man has more than 250 previous fraud convictions, Senior Sergeant Rupert Friend said.

His normal pattern is to ask people for upfront payment for fish from his catch - then never return.

"Usually he says the boat is coming into Raglan and his most common claim is that it is crayfish he has for sale,'' Mr Friend said.

He often targets commercial and retail premises claiming to have already arranged something with another staff member.

"Please be alert to scams such as these and never hand over money to a person you don't know, especially on a promise that they will come back,'' Mr Friend said.

"Even if they can quote names of people who work at your premises it does not mean that they are legitimate.''