Actually, Rat Race Rebellion is a legit site that screens the jobs before they post them. Many people have found work through them, and they have several posts on how to avoid scams.
Some of the jobs they post are no longer available, but I haven’t seen anything yet that looks shady. As for idealist.org, I assume they are legit since RRR links to them. As always, though, you have to be careful online.
What I suspect is the users pay very low wages or pay on a piecework basis, Okay if a person is desperate for any kind of work or just starting out - and there’s certainly nothing wrong with that, but not much in the way of a career.