You need to navigate this question carefully as some have the “customer is always right” mentality and event planning is a people-centric role, where customer service is key. They want to understand how you would deal with high pressured situations and navigating customer needs in line with company policy so focus on your resolution and how you dealt with it more than the actual issue at hand and NEVER bash a client or attendee, directly or otherwise.

To prepare for a job interview spend some time thinking about past scenarios and experiences and what you learnt from different situations, such as dealing with difficult clients or irate attendees.