Several customers lost thousands of pounds to credit card fraud after visiting a Kenilworth shop in the last month.
Jaz Singh, who ran the former Simply Fresh branch in Whitemoor Road, said criminals had placed a tiny device on his card terminal in October.
As a result, he said around five or six customers had their credit card details skimmed. The fraudsters then used their details to spend thousands of pounds.
The victims' bank statements showed that Simply Fresh had tried to withdraw large amounts of money from their accounts, which was how the fraud was detected in the first place.
Jaz said PCSO Craig Ricardo of Kenilworth's Safer Neighbourhood Team had visited to find and remove the skimming device, and said the terminals have now been changed.
Jaz added: "This could happen to anyone. It's very hard to explain to our customers.
"But the device has been found, the terminal's been changed and it's all been sorted."
A spokesman for Warwickshire Police said: "We have received a report that a card machine at a shop in Whitemoor Road, Kenilworth, had been tampered with.
"We have seized the machine, offered advice to the shopkeeper and are carrying out enquiries."
Anyone with any information about the fraud should contact Warwickshire Police on 101, quoting incident number 108 of October 25.