Searching for a Lien on a Patent

Does someone have a checklist that they could share with me on the due diligence that you may go through in the process of purchasing a patent? In particular, I’m thinking about the title search to ensure that the seller is in fact the owner and that there are no liens on the patent – e.g., that the patent is not currently being used as a security interest. How do you go about doing those searches? – Dennis