This is slightly irrelevant - but my partner did a thesis paper on this topic exactly - 'How much do people think their home is worth?'.
She had a subset of data collected by some agency - where people estimated their house value, got it valued/went to auction, compared the results.
From memory her conclusion was that on average, people overestimated their property value by 8-12%.
But then again, there arent many rich academics!
Heh heh - yes, I was once a poor academic
This brings me to wondering what the 18months of valuer education actually gives you! Exactly what makes a licensed valuer any better than any other sensible - note the word - person in being able to pick a value that the property could sell at.
I'm still waiting at a hint of an "acceptable methodology" if there are truly no recent sales in the vicinity that are at all similar - I don't need to here the secret squirrels detail that 18 months of training gives you, but can a valuer on here give something pls?
Rob