Yes, a contractor can insist on selling a house as "voetstoots" when it is an existing home. Only in a case where you have a new home built and there is a building agreement between the owner and builder it will not be "voetstoots".
Voetstoots, means that you purchase the house as you see it. It is a good idea to add a clause to your agreement that you have a period of at least 14 days to submit a "Nags List" which will be fixed by the seller, at his expense within a certain period (say 14 days after receipt of the list).
The purchaser must make sure that the house is enrolled with the NHBRC and also obtain the "ORIGINAL ENROLMENT CERTIFICATE" on that specific property. This certificate is also your warranty on structure for 5 Years and roof for 1 year.