Cass sighed. 'And yet at least one of these people sold a potion dangerous enough to make a woman bleed to death from a small cut,' he said, leaning back in the chair with a tired expression on his face.
'I know there is a reason we don't go after them and I wouldn't suggest it but one of them are almost as responsible for Rosmerta's death as Dennis Creevey is.' He bit his lip. 'I don't know, it's not an easy call to make, but if they sell a potion this dangerous no questions asked, what do they more sell? Poison for the man wanting to kill his rival? Polyjuice to thugs and criminals so they won't get caught? Fake Wolfsbane to werewolves so they think they're safe when they're not?'
He sat silent for a while, pondering the situation. 'We could test them of course,' he then suggested. 'See if we can get dangerous things off them for the right price, only take in the ones willing to sell those.' It was a compromise, as he too realised it was not only impossible to close the entire black market down. The economy would collapse if they even half way succeeded.