Isn't the problem with these marketplaces that most projects are for like $5/hour, while rates for "real professionals" are more like $100/hour and (sometimes way) up?
I am hiring there and I certainly have to pay way more than $5 per hour. My experience is that the price for software development starts at about $25/hour. That is for a student with a little bit of experience and rather low morale. Devs with actual work experience start at about $50 per hour. Again, morale will be kinda low at that price. For a really smart, motivated dev with a lot of experience, you have to pay more.
Well, low quality work. Yes. But, unlike you, I have only internet hearsay as sources.
I wrote an article about getting decent rates a while back...