The recruitment team get to see someone for a few hours over a few days. They get 40min to see them operate the SIM on a profile that the candidate already knows. To tell everything about someone's past in that time is impossible. Reference checks are the only help, but doubtful true references will be given if something is dodgy. The recruitment team do a great job. So do training, some DEC don't pass the course if they don't make the grade.
It's not rocket science. If you feel disrespected because companies aren't falling over to make you a DEC I suggest you may need to Harden up.