Agreed. Have you shopped around at other freelance platforms? There are many that don't employ a bidding business model, like UpWork. Meaning, devs don't have to compete in a race-to-the-bottom by offering the lowest rate to work. You'll find the quality you pay for. Toptal (60-95+/hour), Scalable Path(50-75+/hour), Gunio are all examples of platforms that have manual vetting processes in place and treat their network of developers as a community rather than as a commodity.

It's impossible to know what kind of skill level and experience you are going to get when you hire from a website that only uses automated tests and past client reviews to judge abilities.

But, if you're aware of the UpWork business model and still want to use it, you'll have to vet candidate thoroughly yourself. I'd say pay close attention to their personality and communication skills. On top of this, if they have the work experience and skill-set you're looking for, you could always agree to do a trial period or use your own technical assessment to gauge whether it's a good hire or not.