Turn over to Costco management. If you don't trust them the turn it over to the Police.
No I wouldn't know. Sorry & hope you find him and that's rely nice of you to try to locate where he's at to return his wallet back to him! Great Job 👍
Call Costco
Call or go to location
I agree with all the comments made.
They should have a lost and found area to drop it at.
Go inside and ask for a manager. If possible have the employee meet you in person.
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