Peg Newman, a partner at executive search firm Sanford Rose Associates, described the strangest post-interview deal-breaker she’s encountered. She thought she was hiring a talented engineer who matched the skills and requirements of the job.

“During the offer phase the candidate provided a copy of his college diploma and his professional engineering registries,” says Newman. “When it came to final third-party verification, which required his Social Security number, he refused to give it.”

Red flag. “Upon further verification we found he had used other engineers’ license numbers on the resume, and had dummied up the college diploma. We rescinded the offer with a phone call and a letter,” Newman said.

HR professionals, recruiters, hiring managers and small-business owners all have stories to share about those deal-breakers — quirky, weird or unprofessional things candidates did after an interview or after a job offer.

Karen A. Young is the author of “Stop Knocking on My Door: Drama Free HR to Help Grow Your Business.” Eleven years ago she started HR Resolutions, a full-service consulting company serving clients in Harrisburg, Lancaster and York, Pennsylvania. She lists some of her biggest post-interview deal-breakers:

1. Not disclosing something in your background check: “Tell me before so that I’m prepared and can discuss the implications/complications in advance,” Young said.

2. Disclosing needed vacation time after the offer: This is a no-no, says Young. Reasonable time-off requests are expected when someone is changing positions, but be reasonable.

3. Falsification of preemployment/post-offer paperwork: “In my professional opinion, there is no recovery from this,” Young said.

4. Badmouthing current or former employers: Posting inappropriate things on social media like “I took this job even though they stink as an employer just so I could get a paycheck again” is a surefire deal-breaker.

Samantha Lambert, director of human resources for New York digital marketing agency Blue Fountain Media, lists her post-interview deal-breakers, and how employers should handle them:

1. Salary requirements change after interview: Set expectations from the get-go.

Reiterate the salary range to the candidate in each interview round, otherwise you are wasting their time and the company’s time.

2. Not authorized to work in the U.S./need sponsorship outside of USCIS timeline: If your company is not in a position to sponsor visas, let the candidate know and be clear that it is no reflection of their skill set. If your company does sponsor, but it is outside the timeline, you should ask if you can follow up once the window to file presents itself.

3. References do not check out or a bad reference is reported: Set up a time to speak with the candidate to talk through the negative reference or feedback received, as you never know why or what happened. Give the individual the benefit of the doubt.

Newman lets candidates know that upon offer and acceptance, and once they have given notice to their current company, a final reference will be required.

“Good people understand that companies have a process for employment, education and related certifications and licenses,” says Newman. “So they are generally pretty forthcoming.”

Employers who need to rescind an offer should include a “back-out” clause in the offer letter. Say something like this, says Newman: “This offer is contingent upon satisfactory completion of a drug screen, background check and reference check. If any of the information provided proves to be false or inaccurate, the offer may be rescinded at our discretion.”

When you have to rescind an offer, be brief and specific, says Newman: “Unfortunately because of X we are going to pull the offer.”