When we built our home the inspector did a second look ‘because it was unique’. I think the taxes are based mainly on sq ft (ours is second smallest on the street and second lowest in taxes). The houses next to us are 3x the taxes probably because of sq ft, not quality. Because of the windows and open concept our house appears much bigger than it is.
Valuation methodology varies by jurisdiction but generally the objective is to determine market value. Accordingly, most jurisdictions consider square footage, amenities, views, condition, etc.
Although this isn’t universally true, many jurisdictions perform a rolling re-assessment ,whereby one neighborhood might be re-assessed one year, and another the next, and so on down the line, with every property getting a thorough re-assessment every ten years or so, and all properties getting an annual statistical adjustment to keep up with inflation.
They can ask in our area, but no one lets them in. They are technically supposed to base on square footage and lot size. and comparable sales data. If you think you were assessed to high, there is an appeal board. We are “reassessed annually” but they don’t visit the neighborhoods every year.
If they simply went on sales data, we’d be in trouble, considering the big house on the corner that’s changed hands multiple times. Our street doesn’t have easily comparable properties in this pocket of our part of town. Our eval is based on more than lot and home size, we get separate evals for land and house. Topography, age of improvements, quality of construction and other factors do matter.
“Quality” is a nag. All the older homes tend to get “average” or something like it, just because it’s older materials. Has no effect on value here.
When we added a deck, our fire assessment went up (the town sent special letters saying how much the taxes funding our fire station were).
Our house went from above average to above above average at some point - I guess because we were actually maintaining it :))
My take: there are three aspects on whether it was a good idea to let this person in.
- As others said, do your state and local laws require it? Too many flavors of that for me to comment.
- Also repeating previous voices, was it safe to do so? You obviously had notice, documentation, and a sane level of vigilance about her, so no problem there.
- Will it lead to a higher assessment? I think this question should drive the decision whether or not to make improvements, not whether or not to let someone from the locality see your property.
IMO the only determining factors about whether or not to allow entry should be the first two above.
Going down the rabbit hole of the third reason I listed, we pay around $6,000 annually on a 28’ x 28’ two-story home with a walk-up attic, no outbuildings, over 3 acres of land. When my mother was living with us, she suggested and offered to pay for adding on a first-story master wing. As soon as we told her our concerns about keeping up with the increased property tax that would result, she agreed it would be a bad idea. Sometimes, though, you have no choice and have to go ahead with a reno or expansion. Many of our friends have felt the ongoing weight of increased tax assessment. Hope your situation is a wash at worst; our porch / deck / patio areas have negligible impact at best. 
ETA: OMG I first wrote “walk-out attic” instead of “walk-up attic.”
@HouseChatte, reading your post I suddenly had a case of property tax envy. Where we live, that number is multiplied many times for our two story home on 1/2 acre. As my father used to say, it’s not always what you have, but where you have it. Our decision to leave our suburban community will be based heavily on the impact of those property taxes as we get older, especially since state and local taxes are no longer deductible. @VeryHappy, the situation in our town was similar - many letters from the town, notice of the assessor’s visit and proper identification. Most everyone I knew let them in because if you didn’t, assumptions were made that led to erroneous assessments. Yes, one could appeal but it was faster and easier to let him in.
Ooooh, yeah, I forgot that state and local taxes above $10K are no longer deductible. We currently pay a little bit above $12K, plus a few hundred on our cars, so the taxes going up would be a real bummer.
We are both virtually retired – DH teaches tennis (not lucrative) and I work around 200 hours a year these days. We love where we live, as well as the house itself, but if the taxes go up we will need to reassess.
@HouseChatte: There are a few people that I wish had a “walk-out attic”!! I’d lead them up to the attic and let them walk straight out.
Ditto. We got advanced notice via mail of when they would be coming. IIRC (it was a few years ago) if you weren’t going to be home they would just do an outside walk around. We had to do a correction when they listed part of our basement as finished when that part was storage. We just got notice in the news of a property tax hike 
City came by to inspect a bathroom when we filed a permit to work on it. We actually had to make the walk in shower smaller because of leak that had developed in drain pan so it helped to show city that we hadn’t significantly improved the bath. We also appealed a tax appraisal based on square footage. We have walk-in attic space upstairs in our story and a half. The city had it included in finished and heated square footage so our taxes went down.
On the final reports, our assessment rep ignored that several of us on my street have a finished 3rd floor. We don’t hide that we have that living space. And it’s on older records.
An inspector for our property tax dept. showed up unannounced twice, supposedly to see the new pool, and was clearly annoyed to find our gates locked. The pool (and fence, gas lines, etc.) had been inspected multiple times and was well documented. I emailed him a photo, similar to one taken by a permit inspector, and said I was sure that would suffice. It did.
We realize our taxes are low compared to other parts of the country, but we still think we’re overcharged compared to our neighbors. The tax dept. does not allow appeals to be made by mail, but requires homeowners to appear in person which hasn’t been possible for me for a while. Now that dh is retired, I hope he will give it a try.
I would think any inspector would be pleased that you’re keeping the pool locked and inaccessible while no one is home.
I cannot imagine how peeved DH & I would be to learn that a county person showed up unannounced and entered our back yard without notice or permission. We value our privacy, I know, I know, not doing anything wrong, what do I have to worry about, but I hate big brother, or anyone else, watching me.
Several years ago our then city did reassessments as per laws. This included seeing inside houses for changes. Numbers of/types of rooms (eg baths) mattered, finishes did not as those could change easily. Some things would not need permits that do affect the house’s value. Being given written notice was appropriate and so was letting the inspector in. You saved your own tax dollars by making the process efficient.
I have to say I’m a bit shocked. I’ve never lived in a place where tax assessors would go inside someone’s house! I guess # of bathrooms or “quality” of house interior isn’t counted in places where I’ve owned homes. Phew.
OTOH, I would be afraid of our insurance company sending over an inspector. They value our house at way above market value as it is, so if they see a new toilet they will see $$$ for themselves!
Insurance should be priced on rebuild cost, which may or may not be anywhere close to market value.
Our state doesn’t send assessors or appraisers around unless they’re fighting an appeal made by a homeowner. It seems there is an increase in property values whenever the city needs more $$$ and voila magically gets more in taxes without having to raise % assessed.
I may yet appeal the # of bedrooms and square footage but then again I may not because the guy who bought the house next door as a tear down built an ugly McMansion and will likely try getting mega-$$$$ for it. It may raise house prices for our block and neighborhood. So far, there has been no open house I’m aware of, tho the house appears to be done and the grass and yard he installed is being neglected.
The assessor had to work hard to look at our cabin! There’s a locked gate at the bottom of the hill, so he had to hike up a very steep gravel road, about a half mile long. We were impressed that he tried that hard. We have our land in “tree growth,” so it’s not taxed much. The state checks to make sure you’re not cutting too many trees. Even with a good-sized cabin and 48 acres of land, we have to pay only $600/year in property taxes. Of course, we get no services there! We can’t even insure it because the nearest hydrant is probably 20 miles away.
interior home inspections for insurance are usually reserved for the high net worth segment. As someone said, rebuild cost is not always close to market value. It’s a pain in the butt conversation to have! Most insurance companies do send out inspectors but they only take a couple of quick outdoor photos so you may not even know it happened, unless they see something they don’t like!
I don’t like talking about property taxes…my user name should tell you why! : (