How does Zillow/ Redfin caculate price estimates?

[Randy Dulac]

I am looking at a property from a wholesaler, that is in a good neighborhood.  Its a 2/1 and 904 SF.  I know the area that it is in and most houses that fit that description are around $215k-$230k.  I found the actual house that the wholesaler has under contract and Zillow and Redfin have it at around $155k.  It's the cheapest house in the neighborhood by far.  Supposedly the house is built from a railroad car, but it doesn't appear that way from the outside.  Is the low price because this would be considered a manufactured home?  Would Zillow redfin take this into account?  Finally I know that comps are better than using Zillow, but I was just trying to get an idea of the value.