Hi ZoeT,
I passed it also.. To answer your question, I am also using an agent but for me, it wasn't the agent who helped me get the positive skills assessment. It was from printing off their own guidelines and reading and re-reading and re-reading everything they asked for. AIM give very clear instructions as to what they are looking for to be able to give a positive assessment and once you conform to those and add as much supporting documentation as you can, you would be fairly assessed. All my agent did was read it for me and lodge it. I had to get all the documentation together that they require myself as no one else can do that for you. To be fair, I'm sure if my agent had felt it wasn't good enough, they would have said so before lodging. But the actual work that goes into it had to be done by myself. I found the internet to be a great source of information on how to put it all together also. Once I had gone over their requirements, I put together an excel spreadsheet of all of the specific docs they asked for, eg organisation charts, job descriptions etc. I then added all the extra docs that were personal to me to support my application, eg references, education certificates, course prospectuses, CV. I detailed who needed to sign off on each one, as per the AIM guidelines and worked my way through the list. If you have a good HR department, they will make your life a lot easier..
Once it was lodged, I got my result in 4-5 weeks. Just to highlight also, my agent is now much more involved in our process and took over completely once I received the positive skills assessment and passed IELTS.
Hope that helps in someway..
Best of luck with it..