For the last year, my lovely wife and I have spent our free Sundays poking around at local open houses. We aren’t really in the market to buy a new home but we enjoy looking around and checking out what’s available around us. We’ve mostly been using Redfin because they easily have one of the best search features out there.
If you look at the property history for a house on Redfin, it’ll show all the paperwork that’s been filed on that home’s behalf. Listings, sales, contracts, etc. Along with the “event,” there’s a listing of the source and, in some cases, a little note (on sales) – “This sale was flagged as a possibly abnormal transaction.”
Here’s Redfin’s definition of an abnormal transaction:
Redfin flags a property as a possible abnormal transaction when something about the property’s price or sale information seems extremely unusual or unlikely. For instance, a property that was listed for $249,000 but sold for only $249 is probably a case of an error in the sales record. When we detect an abnormal transaction, we exclude the listing from our property value comparisons to ensure the most accurate data possible.
Basically anything weird is flagged as such. Often, it’s a typo like the one they use in their example. In other cases, it’s something unexpected. I’ve seen a couple of these and, unfortunately, Redfin doesn’t explain why it thinks it’s abnormal. Here’s the latest example of a nice house  we were looking at (mostly to take a look at, it’s a bit out of our price range!)
The sale in June 24th, 2002 was flagged as possibly abnormal but Redfin doesn’t say why. I don’t know if it’s because there was a duplicate row (you can see two “sales” on June 24th, 2002) or because the price jumped so much in a little over a year. The home was sold in Jan 2001 for $790,000 and then again for $1.245mm in June 2002. It would be nice if Redfin added that note to say why it thought it was abnormal.