J M's review (“Be careful with these guys”) further down says it all. I don't want to totally put down UpWork. There's still legitimate work there, but it's harder to find, and UpWork simply doesn't care about freelancers.
I worked as a freelancer for oDesk for about three years. I had constant work, I was making decent money, and I felt well treated by oDesk. When I had a question or problem, I was treated with respect. It was a good service.
That all changed when it became UpWork. The other reviewers who say UpWork doesn't care about freelancers are 100% correct. When it was oDesk, I was a top rated freelancers with a 4.99 rating and I had constant work. After it became UpWork, the rating system changed. At some point I lost my Top Rated status but was never notified about it, then after a while I became Top Rated again, but with absolutely no changes in my status. I wasn't working at all during that period. With oDesk, I always knew how my status was calculated. Under UpWork, it's a mystery.
When there were technical problems with oDesk, they responded immediately; UpWork just makes excuses and tries to shift the blame. Their site frequently goes down, but when I've reported it, they've claimed it was a problem with my computer (it's not - I've been a a computer professional for decades and know when the problem is my computer and when it's the site).
For nearly three years, oDesk was the only place I looked, but that's ended. I had constant work with oDesk, but since it became UpWork I've had only one very small job even though I've been looking constantly. I'm still looking for work on UpWork, but I'm now also looking for other sources of work.
Losing oDesk was a major loss for the freelancing community.