I've found the more courteous you are to the CAD office, the better your chances of being treated fairly. If you deny them entry, they will often appraise high. After all, what's the incentive to appraise low? Just let them see what's what, and get a fair appraisal. If you think it's too high, file a protest. [Aside: this is in TX, can't speak for other states]
As far as new const, they can only appraise it for it's current worth, not its ultimate value. If it's 50% complete, then it gets a 50% appraisal. That's the law.
There's an old abandoned shack on our property, hidden in the woods. We call it the Haunted House. One year, it shows up on the tax bill, at $12,000 (value, not tax). I call them, explain that it's worthless, and I'd tear it down but it's more trouble than it's worth They asked to see it. So we made an appt with them, they came and looked at it, realized it was barely standing and had no value, and removed it. All it took was a conversation.
Treat them like people, not enemies, and they're quite likely to do the same to you.
I remember when I first bought a house, about fifty years ago, and got a prop tax bill. Never even knew there were prop taxes. I was talking to my dad, complaining about it. He told me he thinks of taxes as the rent you pay to live in this country. He didn't want to pay one more cent than he had to (he grew up in Depression Oklahoma), but he also wouldn't cheat, ever. I've always remembered that phrase, "rent you pay to live in this country". People always want lower taxes, but how will we pay for everything?
One common "tax dodge" I saw in Texas was that when you built a nice house on a ranch you fenced the house right in with the livestock grazing area. My understanding was that if you fenced it off separately, then it was taxed as a residential house. If you did not, it was part of the ranch and taxed at a lower rate.
Not exactly true. They will always tax a house as a house, even on an ag-exempt property. They will pull out the land and the house from the rest of the property, and tax it at full value, even as the rest is ag-exempt-lowered. It helps to fence off the house, so you can show how little property is not exempt; otherwise they can claim as much as they want. That's why you fence it. But it won't avoid the prop tax on the house.
You can claim any buildings that are used for "ranching or ag" as exempt, but if you claim what is obviously a house, they won't allow it.
Moving to get away from high taxes but they found me. Again them coming on my property, guess they have more power than Game Warden
