It is important to clarify something about the wild and crazy world of Real Estate professionals and today's "online hunter" home buyers. Specifically, I am referring to the HOPE that the information such as the listed square footage is accurate on advertisements for home listings.
Measuring "oopsies" are certainly real and can happen from time to time, but for educational purposes to help give us perspective to what we are talking about, let us look at a few different terms associated with square footage and their meaning.
Total Square Feet = All square footage in the home on all levels, including stairwells, mechanicals, hallways, etc...
Finished Square Feet = All "finished floor surface and heated" square footage.
Gross Living Area = Total of all ground & above ground finished square feet
The original intention in the phrase "information deemed reliable, but not guaranteed" which is at the bottom of most every listing on Zillow, Trulia, Realtor.com and the like has nothing to do with "I can put in poor home listing information all over the internet, and it is just fine, because of this statement on each listing on the MLS".
For a number of years the single largest issue that slows down the appraisal process has been the need for appraisers to do "double check" the square footage when the listed dimensions or totals seem inaccurate, incomplete, or even impossible.
For consumer's and potential homebuyers, let a famous president Ronald Reagan's saying be used on this issue....
"Trust BUT Verify"