Hi. 
Odoo certification is a course.
You have to pay 220€ for a try
Two ways to succeed your certification :
- watch all videos, take every course.
-practicing, leading odoo's project.

I saw colleges passing their certifications. 90 min are enough for all the questions.

I don't know solutions to "crack" the certification, but I am asking myself "Why" do you wanna crack it ?

Even if you succeed by tricks, you won't have issues facing customer's questions and needs. Learning is the real hack