The moment Victor gave the order to Hilda, orders to restrict the trade in and out of Nightingale with the Yōkai and those involved with them…
The Witches were the first to move.
And just as Victor expected, they immediately discovered the problem and tried to solve it.
They didn't even try to negotiate with Victor or anything like that. After all, there was no need for that.
Victor's intentions were evident with this move. Anyone with the slightest knowledge of the market knew what he was planning.
And it wasn't like Victor was trying to hide it either. On the contrary, he'd purposely made his intentions clear by explicitly targeting the Yōkai and their associates.
That alone was a clue enough to know where to look, especially if one took the time to investigate the Yōkai people, they would discover the incident involving Agnes and a specific branch of the Yōkai.