a sheriff's deed only give the purchaser the legal right to the property, but it does not guarantee that it conveys any title. It only conveys whatever interest the debtor may own in the property, thus it does not guarantee a clean marketable title either.
You would need to check your state laws to determine what title is conveyed by a sheriff's deed, mostly you can go thru a title company with title search for any outstanding lien, then back it with title insurance.
http://blog.wenxuecity.com/blogview.php?date=200905&postID=32381
see also. http://answers.yahoo.com/question/index?qid=20090616180226AAhuqUg