It's not possible. No matter how professional someone appears there's always a chance they're a complete flake in reality. The best you can do is determine qu

It's not possible. No matter how professional someone appears there's always a chance they're a complete flake in reality. The best you can do is determine quickly that someone is not a professional, and the basis for that is going to have to be a variety of factors. There's no one thing that will serve as an accurate litmus test all around. Punctuality is a good start, but I wouldn't put too much stock in it. Personally, I think it's way over-rated. For something like an interview, punctuality is important as a sign of respect and for practical reasons... If you interview someone, you should consider punctuality but also bear in mind that crap happens. I once had an interview and I got stuck in the subway, where there are no phone signals. Who's to say if you are writing off a brilliant worker due to bad luck. In terms of normal punctuality for work, I think it's vastly over-rated. Places generally expect you to be slightly early for work, so I don't see anything wrong with the assumption that you will sometimes be a little late. As long as everyone gets to work around the same time, everyone does their work,everyone works their hours, and people are on time for the truly important stuff....I don't see the problem with even regular "lateness". Anyway. I digress... If anything I think how they are dressed is a better indication than punctuality, but that also has problems. You have to look at a lot of things...I would worry less about whether they are a fit for some hypothetical objective mold of "professional" and worry more about how they fit with what you think is important, and how they fit with your culture. All that matters to me is competence, work ethic, and how they fit in with the group....I'll take that over some nebulous concept of "professionalism" any day.