I use
Freelancer to hire coders.
When the deal had been made, money is transferred into escrow which confirms to the coder that the cash is held by Freelancer and will be paid when the project is complete.
If the coder wants a percentage up front before making a start, that can also be accomplished with an escrow payment, so that no money has been paid to the coder until you the customer are satisfied with the work done.
Perhaps this is something that could be used here !?