It is always easy to beat up the candidate at the bottom. They are persona non-grata. Not so with recruiters; let's be honest, most early in their career are afraid the recruiter might blackball you.
That said, there is a huge difference between contingency and retained recruiters.
In a very simplified explanation, contingency recruiters search for jobs, blanket potential candidates with the jobs, then try to sell the responding candidates to the company. The company pays a finder's fee to the recruiter. There is no agreement between the contingency recruiter and the company until the candidate is presented to the company.
Retained recruiters are retained by the company to find the right candidate, and often get paid a baseline or retainer and a finder's fee. These openings are mostly for very senior roles.
I have worked with contingency recruiters early in my career. They tend to use a quantity based or shotgun method, blanketing both companies and job seekers. They do not seek relationship with you or the company. It is a numbers game, and the candidate is just a number (sort of like spam).
The retained recruiter wold is very different. Most are specialized by industry and are familiar with the top candidates. At this stage the candidates have leverage to demand a certain amount of respect, and proper treatment.
And, that is where my contention lies. There is no reason candidates at any stage of their careers could not treated humanely. The notion that we should delight in trapping someone with a lie, is also ethically questionable.