It doesn't matter if their grievances are legitimate or not (and you have no way to tell if they are). It's bad form to trash talk one's former employer or ex.
It's not just me. You will often talk yourself out of getting hired and many will not pursue a relationship with you if you indulge in it. There is nothing to gain by engaging in it.
It's not just you. Virtually every article I've read on interview tips gives this same advice. Speaking negatively about your former employer always reflects negatively on you.
It's not just me. You will often talk yourself out of getting hired and many will not pursue a relationship with you if you indulge in it. There is nothing to gain by engaging in it.