As far as I know, the VRT rebate is issued to the original ROI owner of the car after the paperwork is processed to prove the car has been registered abroad. You would need to arrange this with the seller in your case. It may take a few weeks. Most Traders are familiar with the process as a lot of hi-end cars and large 4x4's exported in the last 2-3 years have availed of this scheme.
A lot of D3's in the South would originally have come from the UK and would have speedo clocks in miles rather than Km like this one;
https://www.donedeal.ie/view/16969481
QUICK SALE Audi A8 LWB Quattro 4.2 TDI