A bid is not the same thing as an offer.
It is not possible for a bidder to place a bid that is lower than the opening bid price of the auction.
If the auction has the "Best offer" option, the seller is allowed to accept, counteroffer, decline, or even just ignore any offer. An ignored offer will expire in 48 hours (or when the auction ends or if it gets a bid; whichever comes first).
When the auction gets a bid, the option for "Make offer" disappears and if there are any active offers or counteroffers, they just expire immediately. The bidding proceeds as if the offer option had never been there at all.