[TopSage]

Let me explain 

HDB appoint a panel of third party valuers on a yearly renewal 
After valuating a property, the valuer will submit the report to HDB for approval
If HDB approve, then the valuer will release the report to the purchaser
If HDB do not approve, the valuer will have to adjust the value and resubmit to HDB again 

from this process, isn't HDB the one controlling the price?