Financial Diligence Tips/Tricks on SMB

How do you guys handle financial diligence on a small business that barely has books (perhaps no quickbooks, or completely disorganized). Any tricks or ideas on how to handle and/or reduce risk? I spoke to a searcher that had a very clever idea...he is having a third-party accounting firm do a 2-year re-do on the books, and if they close, buyer pays..if they don't, seller pays. I think it's a good idea because if the seller really has nothing to hide, then they should be willing to engage in this. Any other ideas or tips welcome.