I would like to see then list specific numbers but they probably couldn't do that without publicly disclosing the address of the subject property. From the article:

"In their initial complaint, Connolly and Mott lambasted Lanham for his “unjustifiably large negative adjustments” to the comparables he selected and, while acknowledging that some adjustment may have been necessary for the subject property’s proximity to Northern Parkway, write that “a negative adjustment of ten percent is excessive and is inconsistent with proper appraisal practices.”

Additionally, Connolly and Mott praise the second appraiser for not choosing any comps located on Northern Parkway, writing that it demonstrates the “illegitimacy of using Northern Parkway as a boundary” and note that the second appraiser only adjusted a negative two percent for being on a busy street—which they argue is “consistent with industry standards.”

2. Sale of House Next Door: On the date Lanham completed his appraisal in June 2021, the house directly next door to the Subject Property was listed for sale for $500,000. It had been on the market for over 30 days at the time and only 10 days after Lanham completed his appraisal, the list price was lowered to $475,000. Another month passed before this property was under contract and finally closed at $465,000 in August 2021.

Lanham’s suit points out that the house’s sale price directly next to the Subject Property was $7,000 below his appraised value. While the Subject Property “had more above grade living area square footage,” Lanham argues that the kitchen of the house directly next door had (A) a kitchen with improvements that made it more desirable than the kitchen of the Subject Property, and (B) an improved sunroom that was not present at the Subject Property.

“Some value adjustments to [the house next door] would be necessary to compare it to [the Subject Property], but the location of [the house next door], on the same busy road as [the Subject Property], makes [the house next door] a good comparable property and the fact that [it] sold for $465,000 shortly after the effective date of Mr. Lanham’s appraisal supports and validates the amount of Mr. Lanham’s appraisal,” reads Lanham’s counterclaim."

Ultimately an actual comp trumps "industry practicies". Ie I could say that typically houses on a busy street sell for 3% less, but if there is a comp at a lower valuation that trumps what happens typically. Northern Parkway is a very busy road so people might discount houses directly on it much more than a typical busy street.

Maybe 10-20% is not that crazy:

https://homeguides.sfgate.com/much-busy-road-lower-real-estate-value-84306.html

In 2009, "The Washington Post" quoted real estate appraiser Wayne Wallace on the matter of property value loss for locations on a busy road. On average, Wallace said he "deducts 10 to 20 percent for a property on a main thoroughfare." The exceptions to his general rule include condo properties -- whose value actually increases when located next to a main road -- and "bull market" conditions, which are much more applicable in 2013 than at the time of the article.