Question for housing bubble blog readers

Blog readers, I am not a real estate pro and don't have insider knowledge of how bogus sales end up in sale data. One reader has questions. Can anybody 'splain this to us? Thanks!

I have a few questions and I am wondering if anyone can help. I have been watching the beach cities market for a little over a year now. We moved here in 2007. We sold our previous home (in another state) and have been renting since our move.

My questions concern homes I had been watching and their subsequent sales. The only information I have has been either been taken from Zillow, Property Shark or both.

Why does a home sell or transfer hands with a $0 sales price? For what benefit and to whom? For instance, one property I had followed, a spec home, had transferred hands, from the builder to a buyer, with $0 as the price. Then magically it was sold back to the builder, for $0 again, and then resold to someone else for the original and full asking price of close to $2 million. No mortgage was listed so I gather it could have been an all cash sale. Yes?

Am I being obtuse and this is normal business as usual or did something funny happen to prop up the comps? I really don't know or understand and I would just like some insight. I've seen this a few times now and I can't seem to figure it out. Thanks.