Hi Shynar,
If you'd like a critique on a manuscript, don't contact published authors on these forums. Instead, use the Critiques board on the SCBWI section of these boards. You can also post that you are looking for a critique group on these boards as well.
Some authors do offer paid critique services, but I would get feedback from others and revise and polish before you do this if you decide to go that route. You don't want to pay $ with too early of a draft, get it as close to ready as you can first.
Agents generally do not do provide feedback on manuscripts. However, if there is something about the manuscript that they love, but feel it's not quite ready, they may ask for a revise/resubmit. (R&R) When I was in my agent hunt, I did get several of those, though none of them lead to my agent. But I know of people who did get their agent after an R&R.