Apple Id activation

hi,

i am running a mobile repair shop I got an iPhone from one customer which is iphone 4 model A1332 IMEI NO.********** , IOS 7.1.2 . I couldn't able to unlock it because he don't have the id and password. According to customer he bought it from third party. So is there any solution for that how to activate or downgrade or anything please let me know.

tthanks

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