That is because they are in the car boot section of the domain industry - not knocking some strangers door offering £10 for his BMW (in his eyes)
If you think a car is worth £1,000, you don't offer the guy £100 when you first ring him - do you really expect him to take you serious ?
I understand the point you're making domainseller200, and I can totally understand how someone offering you a fiver for a domain you know is worth thousands can seem shocking (and a little insulting), however I'm talking about a situation where the domain has no 'set' price, doesn't have an eye opening amount of Local exacts, or anything really that a buyer could justify spending over a £100 for (for example)..so offering $150 is not lame at all in my opinion.
We also have to take into account that not everyone understands or even knows about things like local exacts or a domain names 'brandability' , so to these people, their offer is not meant as an insult to anyone, and I'm sure in some cases think they are offering a fair amount lol.
I would rather take the time to explain why I as a domain seller feel the domain is worth more..and then at the very least they will understand a little more about the value of domains...who knows they may even come back after reading into it, and offer you a decent, and fair price. I can't see any negatives from this type of communication.
I recently contacted a guy and offered £100 for a domain, he came back and asked for £800, I replied politely why I felt the domain was not worth that amount and he never responded back. 6 months later he contacted me 2-3 times, and the last email was to offer me the domain at £80, lower than I originally offered, however I had already purchased another domain so was not interested anymore and explained this to him..
So my point is sometimes sellers overprice, and sometimes buyers seriously under offer, but if both parties give their own reasons for their expectations/offers, then sometimes a deal can still be met, or at the very least the buyer can walk away with more of an understanding about pricing of domains (what makes a domain more valuable), and the seller can re-evaluate expectations of the domain in question.