I got my 190 visa via an agent and they cost a lot - it's probably gonna be real tough to get one of those now, maybe 60-80 points+ depending on job.
If I'm not mistaken, I believe the working visa can be obtained if a company sponsors you, which means they need to justify hiring you over a local in Aus for the job; probably for a very specific skillset.
Could be wrong though and someone can give you a better overview on this.

If you're talking about going through agent to get the 189, 190 or 491 visas - I think it's okay if you have money to spare and no free time. Otherwise it's tedious work but you can save yourself a fair bit of money if you apply yourself, provided you understand what's required. They will also know the process like the back of their hand if you pick the right agent - otherwise you'll just be throwing money down the drain. For myself I was really busy with work and didn't know anything back then and needed to ensure my wife could get the visa too. So I'll say it depends on your situation and free time to research for yourself.

Otherwise if you're talking about going through agent to apply for a job here - it might be easier if you company allows internal transfer to Aus, like two people I know did. They applied to move to Aus and got the roles & then applied for PR here.