Seller did not ship, after I contacted him he says item is out of stock, offered me to choose another similar item, I do so, but no response since. Purchase made 13 days ago. Should I cancel?
You should go to the bottom of this page and open an Item Not Received Dispute.
If the seller does not promptly refund your entire payment, Paypal will and go after him for their money. He will have other fallout, but you will have your money.