The housing organisation Threshold is advising prospective tenants to be more wary when renting properties and never to hand over cash in suspicious circumstances.
The advice follows a rent scam in the Ballsbridge area of Dublin this week that saw up to 30 people conned out of a total of about €35,000.
The tenants had all handed over deposits and a month's rent in advance for a two-bedroom flat, but when they tried to gain entry, the keys would not work.
Threshold says the situation highlights the need for major reform of the way booking deposits are dealt with in Ireland.
However, in the meantime, it says tenants should be more cautious.
"If a landlord is insisting on getting cash, that should be ringing alarm bells for people," spokesman Bob Jordan said.