Someone explain this

[Bob Basting]

I'm working on my first flip. Have found a home and the numbers seem to work out. What's curious is the home was sold at a foreclosure auction in Dec 2016 for $100k. On Jan 17, 2017, the home was listed at its current price of $69,900. Why would someone buy it at auction and then sell it for much less, or am I missing something here? Any red flags that I should be aware of? 

[Russell Brazil]

$100k is the amount that was owed on the mortgage to the bank. The bank took the property back themselves.