Usually they just kinda eyeball it. The homeowner is allowed to protest and say "hey that's super wrong, I protest!" It's a pretty broken system tbh.
We are property tax agents that homeowners hire to do that "protesting" process for them. IF we save them money, we get paid a percentage of the realized savings. If we save them nothing, we get paid $0.00, so it's a pretty compelling offer.
As for conversions, it's extremely hard to track because it's physical mail. But yes, the campaign did quite well!