Traders are on alert for fake £50 notes after two incidents in Dover and Folkestone.
WHSmith in Biggin Street is alleged to have been targeted on Tuesday.
The day before, members of the Folkestone Area Partnership Against Crime (FAPAC) reported the first incident on Sunday after two men tried to pass off forgeries to buy items at WHSmith in Sandgate Road, Folkestone.
An appeal has since been issued in a bid to trace the people suspected of using them.
The forgeries pass the scan test, so extra scrutiny is needed to check they are genuine.
Three FAPAC members each received two forged notes on Sunday afternoon. All the notes carry the same serial number, which is FF16289463.
A spokesman for FAPAC said: “If the suspects have left and you no longer have sight of them, report in the normal way.
“Make sure that you note down everything that you remember about the offenders, and if they do have a car, get the number and a description.”
A police spokesman said: “Police are aware and work closely with FAPAC. Businesses should retain forged notes, give the customer a receipt and report to Kent Police on 101. Investigations are carried out by the National Crime Agency.”
The Bank of England offers advice for retailers at www.bankofengland.co.uk/banknotes/Pages/retailers/default.aspx