Completing DD is influenced by two factors, tasks and time. When the Buyer has signed off on all tasks, regardless of whether the allotted time has expired, you must ask if the Buyer is ready to open escrow. If the Buyer agrees, convert the DD Checklist into an “Acknowledgement of Due Diligence Completion” document, have the Buyer sign off that DD has been concluded and they have reviewed and accepted everything. Keep that document in the file, in case you need it.
In summary, your chances of closing more deals are directly affected by how well you manage the DD process. That process is best handled by an experienced intermediary/broker.