Offer / counter-offer? Audiogon rules

I am a seller. I receive an offer. I immediately counter-offer. The potential buyer declines it. Is the buyer still bound to his original offer for the orignal 48 hrs.?
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Legally, there can only be one offer on the table. So there is no such thing as "counter-offer" it's I offer, you declined, you offer, etc. This is how offer works, here on the web or in real life, FYI.
The balls still in your court. Your offer declined. To me, it sounds like you both know what you wanted and neither agreed. Back to square 1.
All you guys are entitled to an opinion, but there ought to be a rule for the site that everyone knows in advance or it is not a fair trading platform.  This should not be a questionable area, but a known and published set of rules.  Consider a highway speed sign:  should it say drive at a safe speed or---should it have a fixed limit that everyone understands.

There isn't anything vague here. He received an offer, he declined. Case closed. Simple. What isn't simple is that he now wishes he had accepted the offer. 
What's "questionable"?  Common sense dictates that once the offer is declined it's off the table.  Making a counter-offer is declining the offer.  You're basically saying "No, I don't accept your offer, but will accept ________".  Do you really need a "rule" for that?