If you are the buyer with an incident of Significantly Not As Described on your hands, the seller is obligated to pay return shipping HOWEVER this is only easily done when both buyer and seller are in the same country.
If you are in one country and the seller in another, give him a price for postage WITH TRACKING for his agreement. Send the item back, and you are supposed to be refunded your purchase price plus this extra amount by the seller.
Make sure you keep track of all your messages with the seller and make sure you use ebay Messages for it. If there is trouble along the way, you will be able to better appeal to ebay Customer Service.
If you are returning the item simply because you don't like it, you pay the shipping, plain and simple. You will have to take it to the post office and mail it at your own expense. Again, make sure you use a tracked service or you will not get your money back.
