Can an accepted offer be a lowball offer too?

Depends on degree of deviation. I once bought an antique radio that was advertised as being in  great shape but the chassis was rusted and the radio was dead. Seller refused to take it back. I was not kind on the feedback. Another time I bought a Nikon lens that was advertised as having clear glass when in fact it was infested with fungus. Seller accused me of trying to return a different lens! Again, I was not kind. These were the only times in perhaps close to 20 years of buying on the net that I felt that I was burned. But if the deviation is not dramatic, I've typically bitten my tongue 

    I bought something here from a popular place i will not say.
I asked numerous times if these were the latest models?
Yes was the response ,I recieved them and they were the previous models from like 8 yrs ago but "new" I pitched a bitch and they returned my money after i shipped it across the border got stuck in customs etc etc. took 3 weeks after i shipped them back to get credited .Ya they got a negative which we battled over. I bought another piece from a member,when i opened it it had some surface scratches on the top .It is in my ht rack and wasnt mega bks so i just shot him a message and said hey its all good but it did have some scratches.he offered a return i said dont sweat it.Another i bought a cover for my tt seller said perfect,when i got it it had minor cracks by the handles,I sent a cple pics he immediatley credited some cash to my paypal .thumbs up ...but if i sell something as described and it arrives fine well we made the deal its my issue if i sold it too cheap

A friend recently bought an integrated amp- spent quite a bit if coin. It was advertised as like  new. He and I were quite surprised at what that seller considered like new. Amp went back, refund issued 

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

Because evidently you have regrets too, as the buyer.

I made an offer on something, paid promptly, and received the item which as not in the excellent condition as advertised. I mentioned that and then the "lowball" word came out.

It seems that the seller was not happy with the price, and the buyer was not happy with the stated condition.

Were you trying to renegotiate the sale price after the fact due to your regrets about the condition?

Something different but not too far from the subject. I once bought a piece here, paid for it, received it quickly, condition was as stated, everything worked. Then in a few days I got a message asking me to sell it back to him for the same price. I politely refused. Later in about a month I got another message with the same request. Both messages were short and polite, no explanation was given. This time I decided not to reply. No more messages. He did sound to me like he very much regreted selling it but for whatever reason had to. For some time I felt like sh-t a little bit about this story but then got over it. Still, there is a residue.