My customer returned a mobile they dropped and smashed, what should I do? – ParcelBright

Rarely does a guarantee cover human error such as dropping. If it is covered in your guarantee or warranty, compensate your customer always allowing the option of a full refund option as required by distance selling regulation.
If the damage is not covered in your guarantee but might have been damaged in transit you can still investigate claiming that.
Alternatively if you have reason to believe the event is suspicious then you can treat it as a dispute.
Always check applicable coverage and guarantees that might recover your losses in the event of damage.