There are good agents.
I know several, but unfortunately, they're outnumbered literally hundreds to one, by people who...
a. keyword check, because they don't even know what the requirements mean. They could be selling houses, or washing machines in some high street retailer.
b. know so little about the guys they're after, that they ask you questions like "I see you wrote a bespoke rdbms kernel in ram, to handle trades at high speed, but it doesn't mention that you did sql there, can you do it." or "I see you say you've underlined the every, in EVERY version of <whatever>, does that include version X?" or "I see you designed an enterprise service bus there, but it doesn't mention XML, could you just make it a bit clearer that you did XML, it's not me, it's their HR department."
c. want you to write the sentence "I have full lifecycle experience" rather than describe your full lifecycle experience, because they simply haven't a clue what to look for in a cv when asked to source people with FLC. The same is true of everything else that isn't a discrete skill.
d. and while we're on discrete skills, ask you "How many years of Java have you got." - And when you respond with, "I know people with three years Java who are better than some with ten years, because they're 140 IQ." they respond with "well is that three or ten or something else?"
e. say, "I know everyone else says they will, and they never do, but I will ring you back even if you're unsuccessful."
f. say, "I just want to find a bit more about yourself." or "I have a job that might suit yourself." These sentences aren't even valid English. There's even an agency who puts forward helpers to candidates going to the FCO, with a sentence that says. "It's 'we were' not 'we was' and 'I done it' is never right." How can they be sure when they use the word 'yourself' incorrectly.
g. leave emails saying, "I have a job, somewhere in England, with some skills required, are you interested?" or "PLEASE CALL ME URGENTLY, IT'S LIFE OR DEATH!" and then they've no idea who you are. or send out two, three or four identical emails five minutes apart, just in case you might want to read it more than once. (Thanks to Steve Martin for that one.)
h. leave emails saying "I see you're married, and running the gas and oil analysts at JP Morgan, have two kids, and your wife runs the Equities desk at Goldmann's, and have lived in Hampstead for several years. I can't persuade you to relocate to Benbecular can I?"
As such, I take Shmirsh's view, although I can't always avoid the agents, I just get them to send every cv, and do a five minute phone test, to test whether the guy's stupid or not. (I'll obviously not give the real questions out.) but I can get through a hundred or more people in a morning.
Q1. Where did Labour go wrong on education policy?
Q2. Where did Labour go wrong on Industry?
Q3. Where did labour go wrong on the economy?
If they can't speak english, they fail.
If they can't understand the question, they fail.
If they can't think of an answer, they fail.
They can even get the questions wrong, and pass, if they thought them through cleverly.
The CV, under pressure from agents and HR, is now two pages, which is worthless. "Worked on Amazon" could be anyone from the tea lady to the M.D. Also worthless are references from someone you don't know, so you might as well treat them as such. Just use it to get the name and telephone number for the IQ test. I've seen CVs from people who said they worked on projects I've built from the ground up, and have no idea who they were.
I've heard of one referee once describing a guy as being able to think his way through a brick wall, and even if the referee was right, I still don't let them through the door for a main interview without passing the phone one first, though I'm sure to only ask general questions on the phone, never tech specific stuff.
I can only explain what works for me, and this is how I see it. It's worked for me so far.
In truth, it's not the fault of the agent, it's just life. When you take away industries that average people can do, and introduce an industry that only 2% of people can do, the average guys have to do something for a living. So the government invents loads of non jobs. The world wasn't evolved for ICT.