check public records to see if ownership has changed.
@China Sistrunk : What are you trying to do ?
If you are planning to research every property to find out if they were sold or not,
I think it will be a very tedious and ineffective way of prospecting.
Make sure to do a quick google search -> Your City "County PRoperty Appraiser Site" -> then input the address and find out if the property was sold or not. Not sure about your area though but here in South, FL it doesn't show up immediately so it's best if you have your R/E license and use an iMapp type software and it'll be more up to date with the accuracy of the sale.