From an Islamic legal perspective, it is permissible to sell products that are not inherently unlawful (ḥarām) and that do not contain elements contrary to Islamic belief (ʿaqīdah) or religious principles. How the purchaser subsequently uses the item is, in principle, their own responsibility.
An exception arises, however, when it is known with certainty that a specific individual intends to commit a wrongful act and will use the purchased item for that very purpose. In such cases, selling or giving the item would not be permissible. For example, although selling a knife is ordinarily lawful, if a person seeks to purchase a knife explicitly in order to kill someone, one may neither sell nor provide that knife to him.
With regard to commercial dealings connected to the rituals of another religion, the permissibility of such transactions depends on whether the ritual in question entails something that conflicts with Islamic belief. For instance, if the occasion commemorates the birth of Jesus (peace be upon him), although it is a celebration belonging to another religious tradition, it does not in itself convey a meaning that is inherently negative from the standpoint of Islamic doctrine. Muslims do not celebrate Christmas, as it is a religious festival specific to another faith. Muslims have their own religious festivals and acts of worship, which they observe accordingly. Nevertheless, engaging in commercial and human interactions with others on such occasions is not, in itself, objectionable.
Once selling in such contexts is deemed permissible, there is likewise no objection to partaking in lawful (ḥalāl) refreshments—such as food and drink—offered to those who are conducting sales there.