What's stopping some organization from trademarking the words jeweler or accountant?
I'm an ex-Realtor. The long and the short of it is that it is a term coined by the NAR (National Association of Realtors), used to refer to "Real Estate Agents".
The reason why the layperson thinks it's generic is because it's so commonly used. It has created a brand over product recognition much like Kimberly-Clark has done with facial tissues and the word "Kleenex". And what Gojo Industries has done with hand sanitizers and the word "Purell". And what Jacuzzi has done with hot tubs and the word "Jacuzzi".
It's just like if I were to come up with a title for a designation as a professional domainer. We'll call this title "Domainmeister".
The word "domainer" is a generic term. Therefore, it would be quite difficult for me to secure a trademark on it.
But nobody's used the term "Domainmeister" before. That's because I just made it up. Not being as much of a generic word as "domainer" is, this would make it easier for me to land a trademark registration on the term.
If I only allow those who pass a certification process as outlined by me, pay an annual fee to my organization and so forth, to call themselves a "Domainmeister" they've got to do it. Since I own the trademark, and what I say goes.
This is exactly what NAR did with the term "Realtor". Therefore, any use of it in a domain name, as would be the case with any other trademark, ought to be considered a trademark risk.
See "Internet use" at the following URL:
http://www.realtor.org/letterlw.nsf/pages/TrademarkLogoFAQs
Also, see an example of a NAR case at WIPO:
http://www.wipo.int/amc/en/domains/search/text.jsp?case=D2012-0075