Can an accepted offer be a lowball offer too?

If seller regretting accepting your offer, see if he will take the Item back. It's best to part with the item now then regret later if you are not pleased with your purchase...even at the cost of shipping out of your pocket. 

Why would I return an item if the SELLER has regrets? 

Bingo

I agree. 

I bought a pair of speakers for a price that we negotiated to, I received it (he delivered it), I found a ding or two, nothing major.... his response was "well you did get it for a great deal."

My response was that the price we negotiated was for the advertised condition, not for condition plus 2 dings..  

So you buy something and when received, it is not quite as advertised. Yes, and how does all this play out in the field of Feedback?  Neutral? Negative?  Or, bite your tongue... Positive?