Question about sale price history

[Rufus White]

I don’t know if anyone else has come across this, or knows what might be causing this, so I thought I would ask. While my wife and I are looking for properties, we are noticing that when looking at previous sale prices as recorded in realtor, or Zillow they are sometimes all over the place. For instance, we were looking at a duplex and it states it sold in 2008 for $250k, then in 2009 for $1,035,000, then in 2015 for $559,500. Rent in the area is only $750-$850 per side, and other duplexes are valued at $135k - $150k on the same street, so I am not sure what is going on.