umm you could be in trouble IF
- the phone is stolen as you would be aiding a thief
- there is no receipt
- it has been sourced from grey markets
- or if purchased from Qatar, the name of the dealer/ agent/ etc

insist for
- a receipt
- check if the phone interiors have a Serial No. and an IMI Code
- you should be able to take it to a dealer to have it verified and the seller shouldn't have a problem if the seller can't furnish any evidence showing that it belongs to them.