Is trading and selling herring permissible or forbidden, knowing that those who buy it are Muslims?

It is forbidden to sell herring to those who celebrate Sham el-Nessim; this holiday is prohibited, and selling it is considered assisting in sin, whether the celebrant is Muslim or non-Muslim. Some scholars have deemed it subtly disliked (makrooh tanzeeh) to sell items that aid in the celebrations of disbelievers.