A notice, issued by Dyfed Powys Police, warns of various rogue traders offering general building work, replacing roofing tiles and plastics, as well as some offering to lay tarmacadam.
Farmers Union of Wales Ceredigion county executive officer, Mared Rand Jones, said: “These people offer to do basic work for a small charge but once the job has been completed - if at all - the costs go up.
“They can also get quite aggressive, demanding their cash and will even drive their victims to a bank so they can take the cash out.
“It is illegal to sell door to door and I do not want anyone to fall for their sales pitch.
"If you do get cold callers to your door say ‘NO’ and report the incident to the police immediately.”