What Is An Estoppel Certificate? If you are a landlord planning to refinance or sell your rental property and have an existing tenant, you may be required to ask them for a signed tenant estoppel certificate that you can show the buyer or investor. Estoppel certificates are an important document needed by a buyer or lender so they can have a clear understanding of what is in the lease when acquiring the property. Buyers and lenders need to be familiar with the lease so they can smoothly take over the operations and take care of the existing ten…