Landing a job of any kind at a science festival is a matter of planning to be in the right place at the right time. If, for instance, you are a hopeful future scientist and would like to work during your summer vacations learning and becoming acquainted with your science work, you might seek out businesses that have booths at the fair along these lines
Introduce yourself and make known your preferences. If you have special qualifications make these known, also. And too, if you are truly dedicated in your job search you could have ready a resume in your car.
Another way to getting the attention of those who you would like to ask for a job is have your teacher, or someone else who knows the ropes, introduce you. Then you could put in your application. Even if all this extra-curricular effort does not get you a good job, the friendships and acquaintances you make will be noted and could be useful in the future.
Remember none of this job searching is about trickery or dishonesty, you must be able to put in the time and effort and your pay may not be great, but you will be using it wisely. In fact, the pay may be nothing except a free drink and maybe a hot dog or a hamburger for lunch, but hang in there. It is your future you are building.
Another approach to the job of a lifetime is to offer your reporting and writing skills to the festival leader. Every such event thrives on publicity and you hang in there with your recorder and your camera and put together some interesting articles about the fair. This kind of preparedness will go a long way if your expertise and 'great job' is as a reporter.
Science festivals are nothing more than gathering places where the business of science and the academic scientific community congregate to find out who has what, who knows what, and who is most likely to succeed as the next best of whatever category is up for competition. is a way of letting the know what is going on. It is partly entertainment, partly educational and partly business.
If by your exhibits you expect to make waves and land a future job as a researcher at the newly opened science hall at your school, put your best foot forward and let your talents show. Whatever don't give up, maybe they simply need someone to park cars or to direct traffic, do it. It amy lead to something more to your skill level the next time.