You can't be conned - just ask for 1 months deposit and 1 months rent in advance, and wait until the money is in your account.
You should ask for an IBAN bank transfer, cheques are very 20th century, they should wire the money electronically from their account to yours. It takes between 1 and 3 days for the funds to hit your account once the transfer has been actioned
Anyone naive enough to wire money to someone they havent met could well be genuine.
Obviously find out why they are coming to Ireland, are they professional people, where will they be working, do as many checks as you can, speak to them too on the phone.
With a little common sense and due diligence, you are not taking a big risk by accepting people by e-mail.
Nothing is certain, the word certain should be deleted from the dictionary. The only certainty I can think of is that in 5 or 10 billion years, the sun will get a lot hotter, as it approaches the end of its life. All the seas and oceans will evaporate. Sometime after that, the sun will burn out, and then whatever humans are left on the earth will not be worried about finding new tenants (probably).