Tax Lien Question--Desperate For Help!

THis is my first experience with tax liens, and I am very confused.... I am wholesaling a property that recently wen through foreclusre for unpaid taxes. A company bought the tax leins and want 12,000 to release the lien. My questions are: Does the company need to come to closing or will the closig attorney just cut them a check from the seller's proceeds? DO I need any additional paperwork with this company over and above the contract I have with the seller? Any help would be appreciated!!! :-S