[huehehue]

I wonder if a client has ever set up a scam like this.

They send a fake-looking email to themselves (using existing invoices as a template), then feign ignorance and refuse to pay for goods/services because "we sent the money, not our fault you didn't get it".

Even better that they'd send a few emails saying "we're working on paying you, don't bug us about it" -- payments are harder to collect as time passes for a number of reasons (in my experience).

[captainmuon]

As others have pointed out, it's the client's fault if they have been duped. Although for sure, they'll try to put the onus on the seller, and will claim the seller has been hacked etc..