I'm not an expert on this by any means but I think you've been given strange advice there. Everything I've read or been told states that potential employers are unlikely to entertain an application from someone who hasn't already had their visa granted. I've applied for a 190 to Victoria and we're currently waiting for our visa grant but while we were waiting, we thought that my husband may as well try to apply for jobs anyway (he's a telecoms technician) and, sure enough, nobody seems interested without a visa grant. He was able to contact potential employers and some would happily give advice but not a job offer.
It does, of course, depend on your occupation I guess as some are in much more demand than others.
When I applied to Vic as a teacher I had to register with the teaching association there - I guess to show my seriousness (it cost £150 so you wouldn't apply unless serious!). So, maybe your agent is suggesting that you obtain something to show you're serious too?? Not sure...
As I said, I'm no expert but hopefully someone else 'in the know' will be more able to help you