When we hire engineers, we post in Upwork and several other forums and we go through the identical process vetting candidates, via multiple interviews, screenings, reference checking etc etc.
When we post in other places we have to explain that this is for a "remote" job - and many job posting sites make this very awkward - so in that sense Upwork posting is easier - since all the candidates understand/are remote ready .
However, I don't use the Upwork reference history much (sorry Hayden :-) ) - because there are too few companies that hire their long term staff remote - but thats not an Upwork problem - its "the world is broken" problem.
So this means that reference checking is hard. Shortcuts that we use, is that we trust the hiring practices of certain global companies.
Yandex for example in Russia has very strong hiring practices - this means that an engineer from Yandex is a strong qualifier . Similarly for certain companies from other countries.
I plan to put some of these practices I have learned in a follow up post - because I see how people like you end up getting burned.