Apple Store claims my phone has liquid in it

One morning last week, my iPhone 15 could not use the SIM card, so I went to the Apple store to ask about the situation. After checking, they said it was in contact with liquid and could not be repaired for free. I find it very difficult to understand because I use it very carefully. Not only do I put it in a protective case, but I don't let it get wet in the rain, run, or swim, and I never let it come into contact with liquid. I can't imagine any chance of it getting into liquid. If it really has liquid, it must be some design problem of iPhone 15. So, I really can't accept the situation that my iPhone is contaminated by liquid. However, I can't prove my usage habits.

I think the Apple store should at least give more evidence of how the liquid got in, instead of arrogantly rejecting all requests. I have used 3 iPhones, and I don't think I will buy Apple again.

I don't know what people do if the Apple store accuses you of allowing liquid to get into the phone.