I bought the Deep Black S4 from Flipkart. EVerything was sealed. Only the phone's screen guard had some smudges and seemed almost like a fingerprint (I'm not sure if it's normal). Everything else seems intact. The device has Android 5.0.1 pre installed. But I checked everywhere and this version should come with Kit Kat and we have to update it to lollipop. Could this be a pre owned phone returned by the customer? Should I look for any possible defects? Is there any way I could know if the KNOX is tampered with and made void?