Trading Standards officers in the East Midlands are urging people to make sure they are not being duped when they donate to charity. Flyers are being posted to homes in the region with requests for donations.
But the clothes, toys and other items given to charity are then sold for profit - instead of being given to people in need.
Graham Lambert from Nottinghamshire's Trading Standards said there are simple steps to ensure charities are legitimate.
Fake letters
"If it is not a charity that is easily recognisable they should contract the Charity Commission who can tell them whether it is a registered charity or not.
"There are many good charities that are helping people in need and rely on these sorts of donations, but these (fake) charities are only helping themselves."
Trading Standards officers are also warning about letters demanding money from companies in Derby.
The letters ask business owners to pay �95 in exchange for registration under the Data Protection Act.
About 180 reports of the bogus mailshots have been received in the last year - and letters are completely fraudulent, Derby Trading Standards says.