A veiling is an auction. You can sometimes find announcements of auctions in the paper, for example if a family is about to emigrate and is auctioning off their household items they won’t take with them. Such an auction would be called a boelgoed in Friesland. Sometimes, notarial or voluntary court records were created to record the conditions and results of the auction. These can give you great insights into the lives of your ancestor since it shows you what items they owned.
Auctions weren’t just held to sell items. Sometimes, auctions were used to place a value on the items in an estate of a deceased person. The heirs were usually the main bidders. At the end of the auction, the total value of the estate would be determined based on the proceeds of the sale. The money an heir owed for the items they bought would then be deducted from their share of the proceeds.