My view, which has been confirmed over the years by several FA folks, is that you should have a reasonable basis for the value you state. If your annual property taxes state a market value, that’ll often be the most favorable for a homeowner. That’s every bit as reasonable as something like Zillow. The only truly accurate way to determine a home’s value is to sell it on the day you file the FA forms. No one expects you to do that. An appraisal might be the second best way, but no one expects families filing for FA to incur that expense every year. Use a reasonable method that you can defend with a straight face and you’ll be fine. (That doesn’t mean that if a school determines you might be eligible for aid, that they won’t second-guess your valuation; but that does not mean you lied about anything).
I believe that applies to determining business value and some of the various other investments that folks have (those that aren’t valued daily and aren’t easily valued—shares in private companies, etc.). Just do your best and have a reasonable basis that you can articulate. There are different methodologies and no one thinks there’s an exact value for some of these things (at least, not one that can be determined without a market). So estimates will always vary. But not by ridiculous amounts.