Check the Construction Industry Register Ireland or a trade body membership, confirm tax clearance and a valid VAT and RCT position, verify current insurance certificates directly with the insurer's broker, and take up references on completed projects.
Ask for the company registration number and check it against the Companies Registration Office. A quote from an unregistered trading name with no VAT number and no fixed address is a warning sign.
Insurance certificates should be current, name the correct entity and cover public liability and employers liability at an adequate level. Verify them with the broker rather than accepting a photocopy.