Does it make sense to "ignore low ball offers"?

There is no point in adding "lowball offers will be ignored" to a listing other than being a bit snooty.  Just ignore any offer the seller considers unacceptable.

As far as following an unwritten code, lowball offers are no different than unrealistic asking prices.  40% of new retail for a used item is in the realistic ball park. Some brands or models can be in demand and fetch more.

Once made an opening offer of 50% of new retail that the seller considered insulting.  Asking price was 90% of what he claimed to have paid and $1K more than retail for the newest model.  There is unrealistic behavior at both ends of the spectrum.

Almost all the lowball offers I’ve received were from members with no feedback or a few with very little. Takes a few seconds to hit decline. This is a business site, nothing personal 

When I sell I try to set a realistic asking price. Do I build in some room? Sure. But say I’m selling and asking $5k but figure the first $4250 takes it. If someone offers me $650 that’s not a serious buyer. And even if we were to agree on a price experience tells me that this buyer is going to be an after sales headache. 

Serious buyers only can be used instead of lowball offer cheerfully declined. But frankly, getting annoyed that someone says they will decline low ballers is silly 

 Whenever I see a seller include the totally unnecessary line... "low ballers will be ignored", I say, it's too late. You've already acknowledged the low ballers by saying that. Fugettabadit!

I just politely decline their offer and thank them for visiting my ad. Takes 30 seconds and why get worked up about it?