If the potential buyer decides not to purchase the property, or is unable to secure financing at the end of the lease term, the option expires. The buyer forfeits any money paid until that point, including the option money and any rent credit earned. If the buyer cannot purchase the property but has a legal obligation to (as stated in the contract), legal proceedings may be initiated.
If the buyer wants to purchase the property, they typically applies for financing (i.e., a mortgage) and pays the seller in full. According to the terms of the contract a certain percentage of the option money and rent paid may be deducted from the purchase price. The transaction is completed at the closing when the buyer becomes a homeowner.