Foreclosure below approx upset?

[Sami Poykko]

Hi, 

this might be stupid beginner question, but I attended Sheriff's sales in Camden Co, NJ on 6/15/2016 and I must admit I did not get a very good grasp of how the auction goes. Most of the properties were bought by the bank for $100, but even the ones that were bought were bought really cheap. See example: bought for $71,000, Approx upset $290,427 and zillow estimate $213,000. What am I missing here?