When customers attempt to purchase alcoholic beverages who decides whether the sale is legal or not?

When customers attempt to purchase alcoholic beverages who decides whether the sale is legal or not? The seller/server. Though the customer needs to be honest about their age and ability to purchase the alcoholic beverages, it is the sellers responsibility to check that the person is actually eligible. The seller will check the buyers ID (identification card) and make sure they are hold enough to purchase alcohol. They have the right to deny the sale if the person is not legally allowed to purchase.