If you received a set of earphones that you believe are counterfeit, you have recourse.
At the bottom of this page is the Resolution Centre.
Open an Item Not As Described dispute.
The first suggestion is to Contact the seller and try to settle "out of court". Basically you want to return the set for a full refund and your return shipping.
If that doesn't work, escalate to a Claim. The seller will be required to send you a Return Shipping Label.
Once you have returned the set, you will be refunded in full.
The eBay deadline is 30 days after reciept. Paypal allows Disputes for up to 180 days after payment. You may also be covered by the 'chargeback' policy of the credit card you back your PP account with.
If a seller is noticed by eBay as having 'too many' disputes, especially for Not As Described items, his selling account may be closed.
You can also get in touch with the manufacturer and let them know where counterfeit products are being sold.