Are you getting ridiculous offers from new members

This sounds like a relatively newish phenomena.    While I have not posted in the forum all that much over the years I had been quite active selling and buying all for my own use since (according to Agon staff)   since 2002.   Not much these days.     I have run into a couple of characters over the years but nothing like what has been reported here in this thread.    I did get a very odd transaction going with a character that joined to buy a pair of 2a3's I think it was and it got very problematic although I did not lose the tubes.    I did get ripped off a bit on a very suspicious speaker driver mishap and UPS would only cover shipping cost and not the damage --- which quite possibly was actually the fault of the buyer.    I ate $100 just to get it over with so thats not too bad.  Only loss ever on here.    Overall  all transactions have been good..   But still have not encountered that  particularly  aggressive and rude behavior that other members are reporting here.      

Respond with a counter offer higher than your asking price

Ha, I have done that before, it was fun. Got a nasty response, don't care.

I'm new... what is considered a lowball offer? 5% off asking, 15% off?
If anything below asking is lowball, then why have the feature at all?

I've watched two offers expire with no response, then watched the item expire only to be reposted with new ending date.

At least now I understand why I didn't see a rejection email. 
I didn't intend any insults. 

PS -  it was a pair of used speaker cables

@dumes    
Don't get discouraged by one seller. Some are likely leery of zero feedback buyers. To me, it is foolish to pass up any buyer that has interest in gear I have for sale. If I have it listed with an offer, then I am leaving some room to my bottom line price. If the offer is reasonably close to my bottom line, I try negotiating. If the buyer doesn't move from their offer, I move on. I have sold multiple times to low or zero feedback members without issue. I always make sure I establish some communication with them to get a feel for them before committing one way or the other. As to the question of what is a lowball offer, I suspect it varies from person to person. Some are obviously sensitive to it. I have come across people like the OP is referring to. I recently had a 15 year old piece for sale that I listed for 1/4 of it's MSRP, yet had seen the piece sell consistently at or above my asking price. I received an offer at 40 percent of my asking price. That is low ball IMO and I just immediately hit the decline button with no comments. I didn't get upset, I just declined. I also agree with the OP that more of that kind of offer is occurring here as of late.