If the developer doesn't accept the defect, then it is 
rejected and comes back to the tester. Now the tester will 
ask for clarification with the developer why the defect is 
rejected. Since everything is based on the Req. documents, 
both tester and developer will have to look at the Req. 
document, validate it and then report it if necessary or 
close the defect.
* This Ans. based on "Interviwe Question for QA Tester" by 
Prakash Nepal