Usually the sellers accomodate resonable requests to make customers happy. In case, the seller is not accepting, then there are different situations.
If you didn't pay for the item yet, the seller cannot cancel it. But, if you request to cancel the order, after 4-5 days he can raise a request with eBay to cancel the order.
If you had already paid, and the seller has not marked the item as "ready to ship", then upon your request the seller can cancel the order and raise a refund request to eBay, which is proceesed in 2-3 working days or some times longer, depending on the bank.
If the seller has marked the item as "ready to ship", then ask him not to ship the order, in that case after 4-5 days you will get automaticaly the refund as per eBay guarantee.
If the seller has already shipped the item, then inform him that you want to cancel the order and do not accept the shipment from courier. After few days of non acceptance you will get refund as per eBay guarantee. But, this takes some time, as too many complications are involved.
