Fraudulent cheques worth more than £16,000 have been presented to businesses in Northern Ireland in recent months, police have said.
Golf clubs, electrical stores and restaurants in Belfast, and parts of Counties Antrim, Armagh and Fermanagh have been targeted since June.
A man entered an electrical store in Lisnaskea, Fermanagh, on July 22 and bought a television worth £600 with a cheque. When staff checked with the bank it was confirmed that the account was closed.
A police spokeswoman said: "Police believe there may be further incidents which have not yet been reported and would urge anyone who believes they may have been a victim of fraud in similar circumstances to contact them.
"Business owners are also urged to make all staff aware of customers using cheques to purchase large quantities of equipment and to contact police if there are any concerns."
Fraudsters have struck in Antrim, Lisburn, Larne, Lurgan and Portadown.