Businesses in Cornwall are being targeted by a scam offering them the chance to reduce their business rates.
"Rating reduction" firms contact businesses offering to appeal against 2010 evaluations for a fee of £500.
Trading Standards said that businesses did not need a third party to appeal against evaluations.
Councils collect business rates every five years to calculate how much businesses should contribute to local authority services.
Stuart Benson, of Cornwall Council, said: "Get advice from the local Valuation Office before you agree to anything.
"Remember that you don't need the help of a third party to appeal and even if you do so yourself, your rates could go up as well as down."