I believe that this site draws from the County Recorder’s database, rather than the MLS database like Zillow does. Zillow does not show sales from developers that don’t post on MLS. Often times, Zillow will say “no sales history” because the house was bought directly from the builder.
SDlookup.com shows you all sales.
I love this site. You can do a lookup of a property and then do a quick review (a la amazon). Then prospective buyers can see what you posted. Every person considering buying in SD should do a SDlookup.