eBay has a liberal return policy that protects buyers from items that don’t match the description. If you purchase an item and find that it is not as described, you can return the item for a full refund including shipping costs.
If the item is below your expectations, and you find when reviewing the listing that it was not described properly, you can return it. If the item is as described, you should return it using another option, such as “doesn’t fit”, “changed my mind” or other reason available.
But you also have the option to request a partial refund from the seller. Sellers may consider a partial refund to avoid having to issue a full refund or ship a new item.
For example, if you bought a new camera, and it arrived with some scratches, you might be willing to keep the item if it was fairly priced. The seller may be willing to offer a discount after the fact rather than have to take the item back and relist it at the lower price.
You and the seller can work together to agree on an acceptable amount for a partial refund, or you can return the item.
eBay’s policy on refund can be found here: http://pages.ebay.com/help/sell/item-not-as-described.html