ive got this problem at the moment,sent some air to air out (not the new ones off ima) and waited 7 days,posted them then next day i got the cheque back bounced.
the buyer says he is sending them back but this was three weeks ago,he is in london but we are collecting a car from down there on friday so he may get a knock on the door,it was £280 as well.
in future iam waiting 10 days now for cheques to clear,fooking tossers ruin it for every one else.

as for contacting ebay you would get more response ringing the local chip shop.