More on this - Toptal does have a much more challenging screening than upwork does. I signed up and had a skype interview with a real human, mostly to make sure my English was good. I then had to take a programming challenge. I think of myself as a reasonably good programmer but I failed the test on my first try.

I haven't taken it a second time yet, but its enough to show that you have to be good to get on their platform.