My question involves police conduct in the State of: Calif.

I bought a small item at a garage sale, along with a few other items, I pointed out the item in question ( it was on a table) and asked how much? he owner told me, i picked up the item, and along with a few other items, made my purchase. They did not issue a receipt, which is normal for garage/estate sales. Fast forward a month or so. I sold the item on ebay for a profit. Now I have been contacted by a detective telling me that item has been reported stolen. Can I be liable in any way for that? How can that be possible? What do I have to prove that I did not in fact, steal that item?