Final answer:
Businesses often offer complimentary items such as a free dessert, drink, or discount to guests celebrating their birthday, which are subject to the establishment's policies and may require proof of celebration.
Step-by-step explanation:
When guests are celebrating their birthday, many establishments offer complimentary items or services as a special gesture to make their day more memorable. While the specifics can vary from business to business, common complimentary birthday offerings include a free dessert, a drink, or occasionally a discount on their meal or purchase.
Some businesses may also provide a personalized greeting or song performed by the staff. It's important to note that these offerings might require proof of the celebration, such as showing an ID, and they might be subject to the establishment's terms and conditions or require participation in a rewards program.