In the real world, the property market in an economy will rise and fall. It is no different in Banqer 😉
All you need to do to simulate a crash in your economy, is reduce the minimum house price in the module. This will then reduce both the value of houses that have already been purchased, and those that are yet to be purchased.
If you are finding there is a large gap between the number of students who own properties, you can create a crash to level out the playing field.