Can an accepted offer be a lowball offer too?

Yeah well, I didn't understand it either

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

I feel the same way but this has happened to me. 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. As far as I kniw I did not force the seller to accept my offer! Seller's regret no doubt. 

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 

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 

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

In a word, NO

The condition issue was regarding a wooden cabinet, which I was able to correct myself using steel wool and some refinishing products.

There were two issues but they are related. Once I notified the seller that all was not well, in that he over graded the product, that was when the lowball comment came out, Seller stood by his erroneous grading and would do nothing at all, apparently since he felt that he was lowballed. Frankly, I was taken aback. It's not like I offered 50% of the asking price. It was somewhere about 85% and if I've made an offer, I am serious and I am always prepared to negotiate. Indeed, I now recall another instance when I made an offer on a DAC. I truly thought the seller was on the high side. I made an offer and did the proposed seller tear me a new one for the outrageously insulting offer. Didn't bother with a counter offer, and I found a local guy with the same DAC- we made a deal and I picked it up. With the first guy, we are not talking about your wife or sister so cut the insult stuff. I just don't get why it's so hard for some sellers to politely decline an offer. 

When I sell I'm scrupulous about grading and tend to undergrade. In this internet trading thing, we have buy one thing going for us- a good established reputation. 

And now that I think of it, neither here on audiogon nor on eBay, have I ever once been asked to take something back for any reason, let alone, for being erroneously described, or have ever had a complaint about something not being quite as described. I'm pretty paranoid about accurately describing something. And I truly believe in karma. And I've been trading on line 18 years or so.