Consumer New Zealand has launched a nationwide campaign against what it calls dodgy door-to-door sellers.

Staff say they often deal with complaints about the hard-sell and exploitative tactics of such traders.

Many cases involve elderly or vulnerable consumers, who are pressured to sign for products they don't want or can't afford.

As part of the campaign, 'Do Not Knock' stickers are being distributed for free.

A recent Consumer New Zealand survey found 70% of its members disliked door-to-door salespeople.

The organisation is also calling for changes to the Fair Trading Act.