I'm not completely clear about the situation.
Is it a conference type event which you pay to get into and while there can sign up for pitch session (or similar) from which you will get feedback?
If so, not a scam. Events cost money to organise, if agents/editors are there offering consulting services they should be paid or (at the very least) have their expenses met. While there are plenty of stories about people getting requests from such events, they are not a way of paying to circumvent to slush pile.
That said, pick your events carefully. I remember doing some research on an agent once and found an online conversation about an event like this he'd done. He was shocked to learn the price which had been charged to the writers and the way it had been pitched to them.
Look up the agents attending on Twitter. Are they excited to be going? Are they looking forward to it? Do they regard it as a chance to connect with writers? Those are probably the kind of events you want to go to, but look on it as having a good time yourself, not getting closer to being published.
That said, Writers & Artists in the UK (the standard volume anybody looking to be published needs to get a copy of) has started offering Writers' Services, including an Agony Agent service. For £25 you can email their agent (newish but legit - one of the books she reps is in my local Tesco) a question, or for £45 have a 15 minute Skype call, for (with my bolding:
Our Agony Agents are here to answer your questions, whether it's; what do literary agents do? How do you know what genre you’ve written? Will agents still look at my MS if I've self-published? Or, how on earth do I sum up my whole novel in just one or two pages?
This service connects you directly with a literary agent of your choice. Whatever your question, whatever your conundrum, even if you’re just looking for a little reassurance, our Agony Agents are here to help.
Now, it is right and fair that somebody is paid for their time, but my face is not amused at this considering these are all the types of questions which get answered on #askagent sessions (7:30pm GMT on a Sunday usually has a UK #askagent session going on).
I've also seen somebody talk about the advice they've been given from this service. I've seen more agents state the opposite opinion on the matter (mentioning the MS has been professionally edited).
So, pick your event carefully. Get judgemental about what the agents do