A number of post offices across Armagh were targeted by a team of criminals in a sleight of hand ruse on Monday.
The con artists entered each of the premises, which were mainly based in shops, asking cashiers to change large sums of Euros into other currencies.
The ruse involved confusing staff members by using sleight of hand to hide away some of the cash they are given before claiming to have changed their minds and handing back what staff believe to be full amount.
Police are today warning business owners to be wary of such tricks.
A PSNI spokesperson said: “Advice would be to carefully count any money that is offered to you and keep it in your possession.
“If the customer claims to have changed their mind and asks for the original notes back, insist on getting your money and counting it before returning anything.
“If you think you may be a victim of this type of incident please contact us on 101.
“If you suspect that this is happening at the time, please call us immediately and try to keep the person there or gather as much information and evidence as you can to help identify them.”