I got replacment from WD It is a 1TB black edition instead of my original 500GB blue.
There is no written mark to specify his is refurbished / Repaired disk.Amsrt check from UDMA shows all parameters normal including power on count which is 1 or 2 only.
Is there any way to check whether this is indeed a brand new retail hard disk or recertified one ? I think during refurbishing all smart and firmware is rewritten so cant conclude from that.
Can anyone pls. throw light on this matter?

Most of the time they put "recertified" on the lable. If you don't see it, most likely it is a new hard drive.
Even if it a new hard drive you will get on 6 month warranty on it or your old hard drive's warranty date.

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Think before you act => Most of the time there is only one chance for recovering lost data !