I was trying to borrow some money using that method before, supposedly I was matched with lenders but when I tried to contact them, they never got back with me, so I am not sure how legitimate some of the people are who claim they have money to lend. I don't think i would waste my time with it again. It doesn't seem viable to me.
I think that's probably were the process will fail. It's one thing for people to say they are willing to lend money when nobody wants it, as soon as they do get a request then they start to change their mind. The sites themselves are probably legitimate, it's the people that are using the sites that can sometimes be questionable.
Depends on the platform that you use. Most of the time, if your parameters are ok (ie. some proof of earnings, high enough interest rate etc) then your loan will be filled.