That's the thing, though. If you make a reputation as the kind of guy who can near 100% spot the good engineers, you will make boatloads of money. An employer will pay you more than $30k if you only do great hires. You do 10 of them with your conversation out to lunch and you've made $300k. That's the low-end.
But no one can do that and the few with high hit-rates act as executive-search agencies where they make a lot more.
But I think I would never interview anyone I've worked with. That just seems like a waste. I already either know that they can or can't do things.