beats a dart throw. And apparently some prefer recent darts over past market data. I don't see very many people selling off all their toys just yet. I meet an awful lot of bikers on week ends. And buyers, typically, are buying with more money down. Further, in my area, those small acreage dwellings are still selling with those amenities. The barn/shop builders are still building. We have a number of them in our area, and I noticed one has a sign offering a job to experienced welders.
We've also see steady sales of large personal storage buildings. Folks finally figured out that instead of renting long term storage at the storage for $50 a month, they could pay $2500 and own an equally large one in the back yard that will last a decade or longer.
You have to look at the market ultimately. And what market data you have varies. Expecting all your comps and all your adjustments to come from very recent "snapshot" viewpoints will lead to errors many times. An isolated single sale nearby last week does not tell me that is the "market". It could have sold above or below the market trend that has been established over a longer time frame. Do some regressions. Do some market studies. The trend falls out and by analogy (proxy) you apply that your problem. Absence of evidence is not evidence of absence.
To extract an adjustment for shop buildings, I went to a rurban development where they were common and I used a market extraction to estimate their contribution. In fact, that market study is incorporated in my Site Improvements and Buildings class. Each succeeding sale has confirmed that those buildings did not suddenly collapse in value just due to economy. The buyer who doesn't want or need one, goes elsewhere. The buyer who finds they want that building, pays a premium over similar property without the feature. Perhaps that may differ in your area. But you should run those numbers whenever an opportunity arises where you can.
Even in vacant ag land sales, I check the ratio between pastureland and woodlot. Distance from pavement and access (easement vs public road) issues. I find that the ratios often remain roughly the same even as land prices fall.