Too many people confuse "bid" and "Best Offer." Those are two entirely different things that the seller handles differently. People who come here and use the wrong term (what does the message or display ACTUALLY say you got?) often get the wrong answer (actually it's the right answer for the question asked but not what s/he needed to know).
A bid is part of an auction. Sellers don't "accept" (or "decline") them (eBay accepts them if they are valid bids: meet the minimum bid requirement as of the time they are received, received before the end of the last second of the auction, buyer is not prohibited from bidding on that auction because of a restriction by the seller or eBay). A seller can cancel any bid up until the auction ends (or eBay might if the buyer is suspended before the auction ends or the bidder might retract the bid for a very short very specific list of valid reasons) but otherwise the bid remains active until the auction ends, at which time a winner and price is set from the bids that were accepted by eBay and not cancelled/retracted before the end. The seller is obligated to sell for that price (if the buyer pays, provides valid address that seller agreed to ship to etc.) and the buyer is obligated to buy.
A Best Offer is simply an offer that the seller can take or leave. S/he can accept it, reject it, make a counteroffer (which acts as a rejection of the offer), or do nothing and the offer expires (at the duration the buyer chose when making it up to 48 hours, or earlier if there is a "bid" placed--Best Offer is no longer available after the first bid on the auction, or when the listing ends for whatever reason). The seller is under no obligation to accept any offer or respond in any way to a particular offer or any offer at all.
I see you have 4 active listings, all auctions with no Best Offer on any of them. You also had an auction that ended yesterday with a Buy It Now. If there is something about the bidder on the King book that makes you uneasy about selling to him/her, you may cancel his/her bid anytime up until the auction ends (you can also add him/her to your Blocked Bidder/Buyer List to prevent future bids/purchases by him/her).Go to the Site Map (link at the bottom of this and most ebay.com pages) Sell Section (use the shortcut at the top--it's a long scroll down) and you'll find the link to that and several other useful seller tools. Otherwise you let it ride and hope there are other bidders to raise the price.