Unless the seller provided new information not in the listing as of when you placed the bid, that is not a valid reason to force a cancellation under eBay rules. You are buying the item AS DESCRIBED in the listing, if it is not as described you are covered by the Money Back Guarantee (including the seller paying for return shipping if s/he wants it back) once you get it and it proves to be not as described.
You may contact the seller and beg him/her to cancel your bid before the auction ends, but s/he is under no obligation to do so nor to acknowledge the request, and neither not responding nor responding that it's OK with him/her nor that s/he doesn't know how is among the valid reasons.
