Hi, Aycoleman --
Actually, you really don't want to rely on either one. If it's a house you're seriously interested in, but you don't want to make a move on it until you're more certain of the size, you can get some appraisers to provide a measuring service for you for a relatively nominal fee. I can provide a referral for you for the Corinth area, if needed.
Otherwise, you can ask if the seller has their old appraisal. This will give the square footage based on that appraiser's measurements.
I hope that's helpful for you.
Family Real Estate Services