What qualifies a "low baller"

It's a combination of things, as others have said. The most common form of low-baller is somebody who offers 60% of your asking price. I have no problem with somebody asking about getting it at 80% of a competitively priced piece if they explain their offer. Usually, when somebody is wanting to give you 85-90% of what you're asking, they explain their reasoning. Low-ballers tend to ask for 60-70% (and sometimes even much lower) and give no context. -Kirk

No set rules for me, but I don't humor buyers when the offer 20% or less then asking price. Guess I don't deal with that sort of thing to well :) Though once I made an offer on something that was for sale after talking to the fellow for a few days, and it was super low- more like a joke- but he accepted it! I was shocked, almost felt bad too. Answering the question at hand low baller comes into play when the deal is only beneficial to the buyer and seems to be screwing the seller- ie not fair market value. ~Tim

some of these guys are resellers looking to pick up your component very cheaply so they can resell elsewhere at a profit. While their offers are indeed insulting at times, I'll normally politely respond "your offer may be considered if no others are received within a reasonable time, meanwhile please consider a more reasonable offer". So far though I haven't taken any of them, as a legitimate buyer has eventually surfaced every time.

I agree with Ozfly and Tireguy that there is no specific
deffinition for low-ball offers. If I feel I have priced an
item fairly - considering condition and what similar items
are being listed at - and I receive an offer say 15% or more
below my asking price, I do consider that a low ball offer.
I rarely consider such offers, as in most cases the item I
have for sale has already been replaced with a better item.
And since I buy all my equipment for cash; I'm usually in
no big hurry to unload anything.
I've also had a number of truly low-ball offers from
dealers who are obviously looking to get some nice gear at
cut-rate prices. I have no problem letting them know they
can get it at their price when hell freezes over!