This happens more than you think. I had a customer call me a few weeks after picking up some laptops asking if I still had a specific one. They do managed IT services, and one of their customers thought they left an SD card in one of the laptops. Luckily I still had it and was able to get it back to them.

If someone gives you the wrong stuff, that is their problem. You don't want to be a jerk about it, but they should come and get them from you.