NO, please do NOT "Complete Transaction" before receiving your item and verifying that the item is as described in the listing. If the item is a code, verify that you can successfully redeem the code before completing the transaction. Do not accept any promise from the seller for completing the transaction.
If the seller doesn't deliver your item within the "Seller sends in" + 1-day time frame, you will be given the option to cancel the purchase. See how you can cancel your order.
If the seller delivers a defective or wrong item, unredeemable code, or falsely claimed to have delivered, you can hold the transaction and open a dispute. To do this, go to the order page and click on "Hold Transaction". In the text box, describe the problem and be sure to attach any screenshots that support your case.
By completing the transaction, you are accepting the item and finalizing the transaction.