I think what hurts here are how the fees are structured. If I charge client $100, the invoice will show this number. This will also be the income I’ll be reporting to tax authorities, so I have to pay income tax on $100, and an Upwork fee will be automatically deducted. I don’t know if they would have a legal way to do this but I would much rather my invoice showed $90 in this case since I never even had the chance to see the full $100.