We had a low offer on our house (about 60% of asking price) and the offerees made reference to the Zoopla estimate.
I was quite shocked to see that the Zoopla estimate was about 70% of our asking price which we had quite carefully considered and which was the mid-valuation of 3 local EA's 
I've randomly compared a few local properties on Rightmove and some seem accurate, others way off. Anyone else had any similar experience? Or it is usually a bit more accurate?