When the stamp duty forms are sent for assessment to Dublin Castle for assessment by your solicitor, there is a part on the SD4(which is sent along with the stamp duty form) which asks various questions, one of which asks if the valuation is at full market value.
If that box is ticked no, then the reverse of the SD 4 asks how the valuation is calculated. They will often ask for a written valuation by an Auctioneer which will be examined by the Revenue official making the assessment.
We do not deal with properties, but we often have situations where individuals holding shares in companies transfer them at say, nil, or minimal value, usually to spouses or children, or brothers, sisters, etc. (Transfers to spouses are exempt) In these cases, we have to submit accounts for the companies which values the shares on either a profits or assets basis. Depending on how the assessor judges the valuation submitted, the stamp duty is due on the market value of the shares.
In a property transaction, it is even easier to ascertain the "market value".
If it was a case that you could just under value the properties, sure why would anybody pay stamp duty?
Also, if it is a case that you try and "hoodwink" the Revenue and it is later discovered, interest and penalties would become due from the original date of transfer.
As well as stamp duty being paid at the market value rate, Gift Tax would also be due by the recipient on the difference between the sale price and the actual market value rate by the recipient of the gift.