When looking for new employment its important to realize that the top requirement on every employer's "requirements list" is: PROFESSIONALISM.
Professionalism isn't something you can show on a resume. It is a characteristic that is only apparent through your actions as you proceed through the interview process with the client. One of the major indicators that someone lacks professionalism is the "No-Call-No-Show" - when a candidate agrees to a set interview day/time and then is not present for the interview with no indication that they were not going to make it. It doesn't matter what the venue for the interview is; in-person, telephone or video, being prepared and on-time showcases your level of professionalism.
If there is ever a time that you are running late or need to cancel an interview, you should always have the name and number of the person you are meeting with, or at the very least the contact information for your recruiter so you can call or email to alert them of your delay and the reason you are going to be late. Barring a major emergency there is no excuse for not providing notice that you are not showing up for an interview.
Typically, as a recruiter, I will give candidates a pass if they fail to answer my call at the scheduled time for an initial phone interview, depending on their reasoning and whether or not they followed up with me quickly. Things happen, we get delayed in meetings, we get unexpected phone calls and so on. This is not the case for a client interview. Client interviews are of the utmost importance. The firm has presented the resume to the client with the assurance that the person is one of the most qualified candidates for their opportunity. This assures the client that the firm has vetted not only the candidate's experience but also personality fit and professionalism. When a candidate no-call-no-shows to a client interview this demonstrates an extreme lack in professionalism. Routinely this behavior will get the candidate black listed from both the client and the recruitment firm, additionally this doesn't bode well for the firm because the client is relying on them to make sure things like this don't happen. Not only does the candidate look bad, but they make the firm look bad as well.
The repercussions of an interview no-show can be felt for a long time after the incident. I've had the experience of submitting a candidate to a job opening only to have the hiring manager respond saying "when I used to work for XYZ company, this candidate no-showed on an interview so we are not interested in considering them for employment". Additionally when a candidate is red-flagged at a staffing firm as an undesirable candidate not only do they lose out on multiple future job opportunities, but recruiters speak to one another. Both consulting firms/staffing firms and healthcare systems keep detailed candidate files via their individual staffing/employment software. It just takes 1 click to mark a candidate as a "DNU" (do not use). One no-call-no-show has the potential to ruin numerous potential opportunities across a variety of employers for the foreseeable future.
If you are unable to make an interview for any reason, take just a moment to either call or email the person you are scheduled to meet with - or your recruiter when applicable - even a one line email stating "I'm sorry but an unexpected situation arose and I need to cancel (or reschedule) the interview. My deepest apologies for this inconvenience" is better than nothing at all. Taking the time to send that communication is all it takes to show you have the professionalism the client is seeking.