What do you do if you get extra items you didn't order from a company?

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I know here on Meh they had an uh-oh before where they shipped people IP cameras instead of LED Lights, common mistake.

If another company, ships you 2 of a higher dollar item ($200+) and you only ordered and were charged for 1, what do you do?

Do you tell them? Do you keep it?

Bank error in my favor?