Final answer:
The seller may bid for the good under auction only if they have informed all potential buyers beforehand.
Step-by-step explanation:
The correct answer is D) Only if the seller has informed all potential buyers beforehand.
When a seller participates in an auction by placing a bid on their own goods, it is known as shill bidding. In most cases, this practice is considered unethical and may be illegal in certain jurisdictions. However, if the seller discloses their intention to bid on the item before the start of the auction, it is considered an acceptable practice.