SQFT difference 30-40% difference, tax record, public data,

[Kyoonbae Park]

Hello all, 

My wife and I are about purchasing a single family home that built 10 years ago, which listed for ~5,400 sqft, I noticed that based on floor plan, it is under 4000 sqft, and although I applied maximum home length * width * number of floor, it's only 4,800, while there is attached garage that is 500 sqft, and 350 sqft balcony on the top floor, which need to deduct from 4,800 sqft  so it would be still just around 4,000 sqft. We have not appraised property yet, and when we do appraised our condo 5 yr ago, of course actual sqft and listed are difference but only about 5-10%, did not expected to see under 4,000 sqft when we considered over 5,000 sqft house. I included basement as well, so I don't think this is because of basement, also my GC pointed out that this property seems just about 4,000 sqft based on his look (he toured property with us) and floor plan. What do you recommend? We agreed on price but did not signed contract yet. Also tax record indicated as 3,787 sqft (I understand this could be differ than actual), and other public factor indicating this property as 3,700~3,800 sqft. I also have 2 more properties are on my list, and they are only difference about 5-10% from listing sqft. Anyone has advice on this case?

Thank you!

Thank you!