Vacant Property and the Right of Redemption in Pennsylvania

[John Lee]

Hello All,

I was interested in a sheriff tax delinquent sale. 

 It says: Even if you win a bid on a Tax Sale property, within nine months of the acknowledgement of the deed, the owner of record can go to court and get permission to recover the property by paying all back taxes and the money paid by the winning bidder. This is called the Right of Redemption. Therefore, if purchase a property through Delinquent Tax Sheriff Sale and invest funds to improve the property in the first year, beware that those funds can be lost. The right of Redemption is only applicable if the property scheduled for Tax Sale is determined to be owner occupied 90 days prior to the sale. If the property is unoccupied or abandoned, there is no Right of Redemption.

How can one determine if the property is "vacant" for 90 days? In other words, what systems are in place to prove this or how would someone be able to obtain this information without actually knocking on someone's home?