Stolen/fake iphone check

[RTR01]

Hello, I found a guy on road near Hyderabad airport selling iphone 15 pro max and apple watch ultra both for 30k claming these were caught in customs. Checked the serial number and its original but imei check is showing as invalid imei but by the usage of phone it's seems original. Any suggestions to check the authenticity?
P.S. wrote this on behalf of my friends.

 

[helloworld]

If those are genuine and even if they don't have invoices or stolen, they can easily get way higher through 'phone exchange' or through third-party apps.

: )

 

[RTR01]

If those are genuine and even if they don't have invoices or stolen, they can easily get way higher through 'phone exchange' or through third-party apps like Cashify.

: )

My friend bought the airpods pro 2 for 7k even after warning him and they turned out to be fake. Thank god he didn't but the iphone.