Considering what some consumers pick, I'm not sure professionalism is so high up in their hierarchy of needs. LOL
You can say someone that gets paid is a professional. But that doesn't exactly work here either, does it?

Someone well trained and highly skilled with a cultivated demeanor who adheres to the dictates of their industry, its laws, practices and standards.
How bou dah? 😀

I think it's someone who knows the numbers, knows the business, for sellers, gets marketing and behaves in a truthful, ethical and businesslike manner. I would say how one presents themself is also a factor. 

That would include but, is not limited to simple things like using spell-check on all correspondence, answering their phone and/or returning calls in a timely manner, sharing their Contract knowledge (and knowing the legal documents inside and out) and having reliable vendors to share with clientele.

Dress the part, play the part and LIVE the part!

I go to the dictionary, I look up "professional real estate agent" and I see my picture.

I think it is someone who does not lie, cheat or misrepresent...(and pays their referral fees).

Not necessarily at the top of the consumers list, because they do not understand the real estate game.

Eve

One size does not fit all and what one consumer looks for is not what another consumer looks for.

It is a Gestalt answer. A question of perspective.

Ditto Candice A. Donofrio and Debe Maxwell, CRS 

Candice A. Donofrio nailed this one.

I love how Candice A. Donofrio described a professional.  I would just add impeccable manners, thoughtfulness and having the guts to NOT work with someone that is not a match.  A

One who understands the transaction process and has local inventory knowledge! 

One who really knows the business and the local market.

Technically, any agent who sells real estate and only sells real estate for a living.

That being said, it's amazing what passes as a "professional" agent these days.

as opposed to ....???????  I guess there are some consumers who have crossed paths with UNprofessional real estate agents..... just sayin'

Peter den Boer As in any other endeavor, a "professional" is one who makes their primary source of income at doing something specific.

The less than 1% of the agents in my market.

Debe Maxwell, CRS gave an excellent response... A professional must also be a listener - and be willing to pause and hear the client...

Someone who knows what they are talking about. Start with that

  They are looking for an agent who will get them a deal.

A person who know their craft and appears to be a professional

I tell a Seller who is shopping around for an agent, if you're going to meet with agents other than me ask them how many homes they have sold. I think results speak louder than a fancy car, a designer suit or a MBA. 

I believe honesty and integrity is what they are looking for, but good luck to them, for the most part.

Peter den Boer A professional real estate agent is competent and knowledgeable with the market.

Someone that has a track record of success, listens, of good character and has tons of knowledge.

Like in the mortgage business, a good Realtor should:

1) Dress like a professional, neat, clean and well groomed.

2) Know your business laws and ethics and never compromise either.

3) Drive a clean, well maintained car

4) Never tell someone you were "Too Busy" and forgot to call.

5) If you do not know the answer, be honest and tell them you will find out.

Probably more, but I think these are the most important.

Knowledge, morals, ethics, caring, licensed? I don't like the word, it means not much. Too broad.

One that knows what they are doing.

Their actions define them.

You have many great answers here. 

I agree with Nina.

I would hope a REALTOR would be a professional real estate agent!