There is no (what) problem.

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First, check whether the password on the back of the mobile phone is consistent with the screen password displayed by entering "* # 06 #" and the IMEI code on the sticker on the outer packaging box of the mobile phone. If it is consistent, it means a licensed aircraft, and vice versa. Second, when the trademarks and bar codes of parallel mobile phones are consistent, it is necessary to check the software part of the mobile phone. Because Chinese fonts contain too much information, most mobile phones use special chips to store fonts, and that part of the program software changed by the computer, even if it is localized in English, has lost the functions of Chinese input and Chinese short messages, so the revision machine can be identified by some subtle features, such as whether it can receive Chinese short messages. Third, look at the appearance. Mobile phones that have been modified or upgraded privately will always leave traces on their appearance. For example, if you want to change a new IMEI code for your mobile phone, you need to change the battery cover and the stickers on the outer packaging box, which will leave traces more or less, and careful customers will definitely see it; There will always be wear and dust on the shell and internal hardware when exchanging old goods for new ones, but new mobile phones will not have these problems.