It's hard to recall a single other instance where

It's hard to recall a single other instance where someone is going around saying, for publication, that they bought and paid for something (Dietl), and the seller is going around saying, for publication, that they haven't been paid. If they haven't been paid it means there's been no actual transaction.

The problem here is that we're trying to parse the meaning of contradictory things being said by unreliable sources on both sides of the deal. The only way I can think for them to both be correct is if the money was paid to a third party entity. That way, Dietl paid and Kay can accurately claim that SFT never received the money.

The only actual solution would be to be able to look at Dietl's company's books to see if they took a deduction on their taxes for the expenditure. And that's not going to happen.