Is it permissible to sell cakes and sweets to a person who owns bars, knowing that the money earned might be unlawful, and would that be considered aiding in sin if customers drink alcohol with the sweets?

It is not permissible to sell cakes, sweets, or food to one who drinks intoxicants, due to the Almighty's saying: ﴿And cooperate in righteousness and piety, but do not cooperate in sin and aggression.﴾ If it is customary to consume this type of cake or sweet with alcohol, it is not permissible to sell it to them or to the tavern that serves it, as it involves aiding in sin. However, if these cakes and sweets are not consumed by them with their drinking, and are not associated with alcohol consumption, then there is no harm in selling them. In case of doubt, the safest course of action is not to sell.