Get them to send you the check.
Say you deposited it.
See what happens.

Offer steam gift cards as the payment for the inevitable “I sent too much” part of the scam. Steam is no longer selling physical gift cards.
So you can waste some time pretending to go to a shop, unable to find them, trying other shops etc.

Kitboga is a master at wasting scammers time if you want some YT vids to watch.