I have used e-lance and upwork to the tune of about $140,000 and in my last year of hiring on UpWork we plugged $36,000 through them. Generally they've been pretty good and usually fast and fair to act, though in all my time of using them I've only had 3 bad experiences, 2 of them were resolved quickly and well, the third was a shit show.
I think a lot of people get screwed on UpWork because someone posts a shitty outline of a job and then expects the world to be delivered for $5. I don't operate like that, we treat it like hiring normally - we thoroughly interview and the spec is very detailed.
The last contractor we hired was for firmware and an issue we had, we needed someone with Rockchip experience and someone who could work on it full time. We explained the problem and the spec of the job repeatedly to him and he agreed. We agreed a fee - a little higher than what we budgeted but honestly didn't care - we were getting this solved.
Anyway fast forward and he has done about 50% of what we agreed - we ask him when can we get the next 50% he said when we pay him more - we said, that's not what we agreed, it's in the contract (on the job spec) in the UpWork messages (again reemphasized) and we agreed over phone calls and emails and he signed. He said he didn't care he wanted more money before he would complete it. At this point the firmware he has done is essentially useless to us without the last 50% so I go to UpWork and explain everything - hoping they would give him a nudge - we had everything outlined on their system - their response - you need to pay him. I was baffled. So I opened a credit card dispute to get the money back.
UpWork's behaviour became down right embarassing. The disputed amount was in the range of about $1000 and they became so hilariously hostile, then angry, then sorry, then hostile, then derrogatory, and eventually demeaning (offering us $50 credit if we withdraw the dispute) we said no. They said they wouldclose our account - we said fine.
How stupid of a company do you have to be - not only that - we had about $30,000 more lined up for the next 6 months - now we just go through our network and other job boards. We will NEVER use them again.