Businesses in Cornwall are being warned not to pay for advertising in publications which they have not agreed to.
Cornwall Council Trading Standards said complaints had been received after businesses received invoices for £149.
On querying the invoice, businesses were then told that the advert was agreed to in February.
Cathy Brown, from Trading Standards, said: "We advise businesses to send a letter denying any contract exists."
She added: "In some instances the bogus advertising company then claim that they have taped evidence of the business agreeing to place the advert.
"Businesses should not be intimidated into sending a cheque by such threats but instead refuse payment."
Trading Standards advised that companies advertising in such publications should check with the charities to make sure the offer is genuine and the publishers are known to them.