This is very important aspect towards your job. There are many ways employer can find you unprofessional but mainly the track your in-person presence or online presence. If you use an unsuitable expression on your public social media profiles or show up for a face to face interview in a bad attire or bad reference from your previous boss to your new employer, beware – you could seriously get blacklisted. Solution: Simple and Straight - Be Professional. Always dress nicely in a suit for an interview. Keep your online image clean or at least try to reconsider your privacy settings, always stay work-appropriate topics both in-person and online. And very importantly be professional and courteously with your employer and everyone in the organization. These are mail 3 reason behind your employer blacklisting you 1) False Personality / Dishonest in job 2) Unethical/Unprofessional attitude towards work 3) Negligent attitude towards work