I've always found these accuracy claims fascinating. They both claim <5% error in my metro area, yet when I'm house hunting it's rare for me to find listings where both sites agree within 5%.

I always check both sites when I'm looking at houses (basically every day) and the pattern holds: They can't really agree within 5%.

Technically they could both be correct if the sale price lands neatly between the two estimates, but some of these historical estimate graphs are also swinging more than 5% per month, too. I think there might be some fuzzy math going on somewhere.