If the item has not arrived after 30 days (from Asia?) contact the seller and ask for the Confirmation of Delivery number. Don't worry if there isn't one, this is just a courtesy.
Do NOT allow him to offer a replacement. Only a refund is acceptable.
If you don't get a number or a refund, on Day 40-43 after purchase open an Item Not Received Dispute - look under Customer Support.
If the seller cannot prove delivery, Paypal will refund you and go after him for the money.
If it arrived, and 45 days have NOT passed, open an Item Not As Described dispute. The seller can demand that you return the purchase (with Delivery Confirmation) before a refund is made.
If more than 45 days have passed, go to the 1-800 Customer Service number on the credit card you really paid with (Paypal is just a mediator) and ask about a chargeback. Cards have longer deadlines, but they do have deadlines, so get on this immediately.