@Kee Barber I've always found $/sf to be very unreliable, unless you're evaluating identical homes like a row house or condos in the same development. 

I obviously know the positives of mine but what are your thoughts of owning 2 pretty identical units side by side?

There’s are also two 2 flats next door that are “legal” that are identical to ours.

Let's say we have identical multifamily buildings, units of 2.

Our neighbors across the street with a nearly identical home said theirs recently appraised for 670, while another similar one down the street sold this winter for 580.

Think of the terms "buyer's market" and "seller's market" identically to when you are thinking about the underlying real estate itself -- does the home have 40 offers all over asking (seller's market), or just 3 offers and all 3 are lowball (buyer's market)? 

I just dealt with an almost identical transaction the other day (sibling in prison included) and the property had a bunch of tax liens on it making it worthless once the liens were paid off.

Neighbor sold two days ago, identical layout for $539k.

These properties are literally down the street from each other and are almost identical except for square footage.

If they also have a picture of your driver license - that's all they need to steal your identity ....