[danfuzz]

You're probably thinking of Prop 13, which, no argument. But I don't think the fix is as straightforward as you imply. (TLDR the biggest problems are due to corporate landowners, not families who own a single dwelling.)

Also, what jurisdiction are you aware of that takes un-accepted real estate offers into account for tax purposes?

[lmm]

My background is Ireland, where there's a general requirement to self-assess an accurate value; you're not specifically required to take offers into account but you're not required to ignore them either, it's more of a "you should assess all the information available and come up with an accurate valuation" type law, with the specifics being left to interpretation. https://www.revenue.ie/en/property/local-property-tax/valuin... has a bit about the process.