It's amazing that just calling someone's landline and then writing a check or doing a bank wire is probably the most secure method you can do when transferring large sums for 100% legit purposes. If they just rang up Gary and said "hey we are ready to pay, how do you want it?", the scam would have been found immediately. You can't really send a check to the wrong account, Gary collects it and deposits it himself at his bank.

Honestly, doing multiple Zelle payments across a several days sounds like a pain in the ass. I would have just mailed the asshole a check and told them to do their own money laundering. That seems incredibly fishy, especially to multiple emails. I would feel very strange about that.