You may be surprised to read this, but firstly recruitment agencies have a professional body who regulate their conduct, and secondly it is possible to qualify as a recruitment consultant, up to graduate level. The professional body is the Recruitment and Employment Confederation, http://www.rec.uk.com/ and members sign up to a professional code of ethics.
At the end of the day, does it matter if agencies are a) regulated and b) professional? After all, very often employers are looking for people to fill vacancies and will go with the source able to provide them.
As a Member of the Institute of Recruitment Professionals, I can say that in order to pass the Certificate of Recruitment Practice, I had to study for about 5-6 hours, do an exam, and undertake CPD every year which consists of attending training courses or reading articles, in the same way solicitors do. As someone who has completed the LPC, the LLB and an LLM, as well as other qualifications including the IFA FPC 1 and 2, the Recruitment Professional qualification is by far one of the easiest I have experienced.
It did however make me stop and think of the service we provide to clients. Very often, existing and older clients will call from the middle of a partners meeting and ask me to give salary ranges for a particular type of candidate, to give market research advice into the current state of the market, or to discuss strategies for longer term recruitment. If someone has a professional qualification linked to that advice, it can only be a good thing in terms of providing quality information, advice and service to clients.