I've used Upwork in the past with no problems (from Upwork, I've had problems with clients). I ready the links you posted and not one of them mentions Upwork cheating or clawing back payments. Only the first article is really critical of Upwork per se, and all the truly damning stuff, if it exists, has been removed, so it's hard to judge.

I'm not saying you're wrong, but you made a pretty contentious statement and your evidence is lacking. Do you have a more explicit link to what you're talking about?