Question: Is it safe to assume that for sealed phones ( with non-removable battery) the phones have not been altered? How do I check that the IMEI numbers match if I cannot open the phone?

This is mostly cos I'm looking to buy an AP HTC One S, but not sure how I can check to see if it hasn't been altered (other than coming in a sealed box) - they wouldn't be able to switch the battery right? Would they would go as far as to disassemble phone...