How is a property valuation done?

Mainstream AVMs (Hometrack, Rightmove, Zoopla) report median accuracy within 5% of sale price on roughly 70–80% of properties. The accuracy collapses on unusual stock — listed buildings, flats above shops, mews, properties on private roads, anything with a non-standard floor plan or extension history. Lenders use AVMs only at low LTV (typically below 75%) on mortgageable mainstream stock and instruct a physical valuation otherwise. For a homeowner running their own valuation, an AVM is a useful starting point and a poor finishing point.

Yes, but the bar is high. Submit a written challenge to the lender within their stated window (typically 14 days) supported by evidence: three to five recent sold comparables on Price Paid Data with full address, sale date and price; photographs evidencing condition; any documents the original surveyor missed (planning permissions, structural reports). The lender re-instructs the surveyor to review. Roughly one in four challenges results in an upward revision, usually modest. Stronger challenges work where the surveyor used distant or stale comparables.