I haven't used Upwork for a while. How much does Upwork charge for freelancer fees and fees to clients?
I ask this because on a local hiring site I compensated a Freelancer for fees in my quote and then found the company charged me for their fee separately as well as my fee.
As a freelancer, they're charged a sliding fee based on their lifetime billings with each non-Enterprise client. This includes all contracts they've ever had with that client. Service fees are the same whether the contracts are hourly or fixed-price.
You don't have to compensate the freelancers, they (should) include their fees into the quote. You may take the fee structure into account when analyzing proposals but that's about it. If anyone asked to be 'compensated', it was just a way to extract more money from you without extra work.