PC,
Two things explain the difference. I search only SD county listings in the MLS. There are lots of out of area listings in Sandicor that ZIP Realty includes and I dont. There is also some kind of a glitch going on with the MLS and about 1000 listings disappeared a month ago from the count in one day. I cant resolve it so I just stick to a consistent methodology. In my eyes, the numbers are fun to look at but the real issue is what direction are they going and how fast.
Hope this adds some clarity to a very unclear situation.