Purchasing property found via contractor assignor

[Brad Stafford]

I recently found a property I wanted to purchase, for 50,000, and the person I found it through is  selling it as a, "Contract for assignment." I have did a title search on the property and it does appear it has switched hands to a private party in October

After I approached the, "Assignor," I informed them that I had cash, and would like to move forward with purchasing the property; however, it seems like he is dragging his feet.

My question is this, do contract assignors need to have a contract with the owner prior to attempting to find the buyer? Or it common practice for them to attempt approach the owner, with a buyer, retrospective?