Ive made a few offers on domains for around £4k for domains I would value at around £6k to £10k. Most of them come back with counter offers of £100k+ to which I just cancel negotiations straight away.
Theres a lot of people who overvalue their domains, I think its very easy too, i have done so in the past with 1 or 2 of mine. Its not just sedo, ive some a few people on here as well. I think some people are dreaming that they will sell one of their domains and be able to retire early.