Lincolnshire Police have issued a rogue trader alert in Horncastle and Woodhall Spa.
A Lincolnshire Police spokesman said: “Two males have been going door to door in a white Transit van - VRM beginning KV10 B - selling fish for high prices and they have also been entering properties without permission and getting people to purchase fish before they will leave.”
Police say the males are from a Durham fish sellers, and are using a chip and pin device to take payment.
The males have been charging people more than £300 for items.
Police have warned residents in the area to be aware, vigilant and keep doors locked where possible.
Report any similar incidents to 101, quoting incident number 164 of April 12.