How can I unlock an iCloud locked iPhone that I bought from a random person on OfferUp

Ask for a full refund.

To unlock the phone, you will need the Apple ID and Password of the person who originally set up the phone. I think you will agree that the chances that you can locate that person are a tiny fraction above zero.

For the future.....do NOT buy a used phone unless you know the person that you are buying from and can locate them at all times.

Ask the seller to remove it or give you a refund, or ask the OfferUp staff for a refund. It's an anti-theft measure.

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