The platform is legitimate. Some people that use upwork are scammers. I have a lot of writers who have said they were left high and dry after an upwork client refused to pay for the work they did. To be fair freelancers can as easily ghost on clients. So, I don't fault Upwork for that. The issue is, though, that Upwork doesn't do much to prevent or stop that.
So, I don't fault Upwork for that.