Hi Ducky
All valuers must work from facts, and if there is a figure from a similar property at a low price he has to use it as he will never know if it was a forced sale or not, the same as one which appears to be high because the buyer was a wood duck and did not know any better
You cannot manipulate prices ( unless you are the government) to get a figure that you like
IF the price of housing goes down more will buy for investment and if some get burnt due to their inexperience well they will learn a lesson at their own cost