Sorry for the clickbait title haha. I recently skimmed through around 1400 hand-filled-out sales disclosure records in a relatively well-organized county, in order to get a feel for market pricing.
This quest started after trying to use Zillow and Realtor.com to gather sales data in order to derive informed offers. I found that there were problems with the alleged previous sale prices on those platforms when I dug into the actual sales records behind the data. For example, it would say a parcel sold for $X, but I looked it up, and it was actually a sale with multiple parcels, and Zillow/Realtor would just divide the total sale evenly by the number of parcels in the sale, even though the parcels were wildly different sizes. This is also why so many small vacant lots are reportedly sold for half a million dollars, having been paired with large single-family home parcels.
I decided to dig deeper, and evaluate over 1000 county sales records over the past decade, which these real estate platforms apparently use for their data. What an eye-opener it was. Have any of you gathered the intuition to guess roughly (without much context) how many of the 1411 sales involved only one parcel? Mind you I filtered out all sales from districts within any city limits. The answer is 555 of 1411. That's fewer than 2 out of 5. Maybe you're not surprised, but I was. 490 of the sales involved 2 parcels, and 168 involved 3. The remainder were sales involving more than 3 (except for one sale disclosure, where the recorder wrote "0" for some reason, even though a parcel id was included).
It would have been easy enough to get accurate comps by just omitting the multiple-parcel sales, but the problem didn't stop there. I skimmed over the sales descriptions, and whoa was it all over the place. Lots of times people are only buying a small interest in a property, or a lot of times, the recorder says there's only one parcel in the sale, but they write down a price that reflects a different property that was part of the same sale, and they wrote it in a different sales disclosure (also with only one reported parcel). Or the sale price was just paying off a contract, where it didn't indicate the previous equity. Or the sale involved eminent domain, where part of the sale was tied in some elusive description of "damages". Or the "sale" was part of a divorce settlement. Or the sale was a neighbor's exchange of parcels, where one party paid an additional amount on top since the property they were getting was more valuable. Or it was part of some kind of even more complicated exchange of personal property and land. And there's the host of all sorts of sales under duress, such as divorce, estate, and even tax sales (where the sale disclosure is recorded after the redemption period is up). The number of "clean" single-parcel sales ended up being very small compared to the number of sale disclosures.
tl;dr: I learned that getting accurate vacant land comps from sales records, especially on sites like Zillow and Realtor.com is a bit of a crapshoot. I'd probably only rely on those under very specific circumstances, such as a particular newer subdivision with a whole bunch of nearly-identical lots, and you're sure that the sales were for individual lots, and the sales were all very recent.