what is the official return policy law of Ireland?

Under current legislation a consumer is entitled to return a product to a vendor for a full or refund or exchange (at the discretion of the vendor) if

a) the product is demonstrably faulty
or
b) the product is not of merchantable quality (ie of shoddy workmanship and not fit to be sold)
or
c) not suitable for the purpose for which it was sold (as opposed to the purpose for which it was purchased)

and

it is returned within a reasonable period of time (usually considered 3 months)

and

with reasonable proof of purchase (usually, though not exclusively, a receipt)

otherwise the principle 'Caveat Emptor' (I think that's the spelling!!) applies, which simply means..let the buyer beware!