"If you have bids on this listing, or if the Reserve Price has been met, you must cancel all bids or sell to the high bidder(s). This does not apply to listings in the Real Estate category using Ad format, as there are no bids in this format"

IMO - ending an auction by selling to the highest bidder IS NOT unethical.

Ending an auction early and canelling bids (obviously to sell off ebay IS unethical.

Ending an aution early with no bids is irrelevant

Just my opinions.