What are the most common mistakes that candidates make in job interviews that cost them offers and how to avoid them?

Answer by Yishan Wong on Quora:

«I’ve interviewed literally hundreds of people, mostly for engineering positions and some in management.»

• being totally uninformed about the company they’re interviewing at.
• for popular consumer internet companies, not having created an account or tried out the product even minimally before coming to interview — shows you don’t do your homework.
• trying to show off and failing. Showing off is a gamble: if you pull it off, good for you. If not, expect no sympathy.
• lying about having been given a question before (by another interviewer) when the interviewer asks if you’ve gotten it before.
• lying in general, and then getting caught.
• claiming expertise on things in their resume they don’t know anything about and expecting not to get asked about them, and then failing miserably.
• swearing, or being excessively inappropriate in other ways.
• being disrespectful to some of your interviewers (I once had a candidate who was respectful to all his male interviewers and totally rude to all his female interviewers).
• outright insulting your interviewers, or really any group of people in general.

• do your homework about the company.
• know what you know, and know how to demonstrate it. This will make you both confident in yourself yet humble about what you don’t know.
• don’t lie, of course.
• be respectful in your thoughts, and it will show in your words.
• go along with them. They might ask you to jump through a few hoops — that’s fine, this is an interview and they probably have a routine. No one ever lost a job because the interviewer said, „Man, that guy was just way too willing to jump through all my hoops!“ If it’s too excessive, you can easily decline the offer later, but it’s not worth it to prove how cool a rebel you are in the interview.»