Two Year Right Of Redemption In California

The civil code here say that an ex deed holder has a right of redemption for two years if the equity purchaser does anything unconcionable in his dealings Can someone come and get their house back easily? Don't they have to prove something untoward has occured ? How much of a problem is this for shortsellers? How often does it occur? Sorry for all the questions but that's the only way I can learn Niceguy