Is a offer of -20 percent on an OBO ad insulting?

What is OBO except an invitation for low offers? An offer of 80% of full price does not deserve rudeness. The buyer may well have gone to 90% or even 100% with a little bargaining.

20% under is not an insult. I listed some speakers a long time ago and got offers at 50-60% with "advice" that I was way overpriced. Those were insults. I kept the speakers, sold them years later for little less than I had paid for them, and recently saw them on Ebay (yes I recognized them from the picture and serial number) for even more. I listed a sub and got offers 20% under, those were not insults. But I kept and still use the sub in my second system. An insult is an insult. 20% under if the seller says "obo" is not an insult

i think it depends on the selling price. if the selling price is low then 20% is too much. i look @ things a little differently. we are a small group of people that "do" this hobby. if you are "doing" the hobby then you know what is a fair price and what is not. to take advantage of someone because they are in a bad spot is not honorable. i would not like someone to take advantage of me if i were in a "pickle". its not all about money. if the person cant afford it then they need to save the money. gee what a concept.

20% is probably not terribly unreasonable. Being a seller myself, I can understand the sellers point of view here. It's exteremely irritating to get many low ball offers in a row. For example, I had speakers listed at 825 for the pair plus shipping. Someone wrote me and said they would give me 500 shipped to their area. I noticed a lot of people don't do research before they make offers. Look at other units similar to what you want and see what they are going for. Then consider an offer.

what a clown...
He cannot block your email, because it was delivered via Audiogon emailer; if he blocks that then he's blocked ALL email from the remailer utility, & therefor will not receive any offers at all. Duh! This seller with no manners whatsoever has just eliminated himself for you, saving you the trouble of finding out after the fact what a jerk he really is. There's no telling what you might have received, very likely *not* in as-advertised condition.
I've received a similar discourteous response at one time & my offer was quite reasonable, esp. compared with the ridiculous asking price which was in fact an OBO listing. I responded back & set him straight. Guess what, no one bought his merchandise & I later saw it advertised on AudioReZoo.