Urgent problem! There are unknown text messages in the new mobile phone. Should merchants return goods unconditionally?

You can return it. According to the Three Guarantees Law, if no one damages it, it can be returned unconditionally within seven days.

You must have signed an invoice to buy a mobile phone. The invoice shows the date when you bought the mobile phone. If there is a text message, generally speaking, the time of the text message will be before the time on your invoice. (Generally, the mobile phone can check the detailed time of sending and receiving SMS. This also proves that this message existed before you bought it. You can talk to the business theory.