If the offer is not totally low-balled I will usually try to negotiate. But, I always respond just to be polite. Are low-ballers a PITA? Sure, but being polite is pretty easy. I always try to remember and take the high road so to speak.
Case in point, just had an offer on a preamp I am selling. The buyer offered a trade for an older pair of Thiel speakers. Interesting idea, but the speakers are worth less than half of what I'm asking for the preamp. I would consider that pretty low-ball! I politely replied that it was an interesting idea but I couldn't do that deal. No sweat on my part. Was the buyer being an a-hole with the offer? Maybe, maybe not. Maybe just looking for a sweet deal.
Let's be nice, people.