Gardai have warned business-owners to be careful exchanging large notes.
It follows a number of attempts of deliberate confusion at in shops and restaurants.
The latest attempted scam took place at a business in Donegal Town in recent days.
It involved the changing of large notes into smaller denominations which also included possible forged notes.
Similar attempts have taken place in Milford and Falcarragh.
A Garda spokesman said similar scams have been tried across the county in recent months.
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