When accepting a quote, you will be asked to pay it immediately. The money will then be locked on an escrow account before the project's beginning. The freelancer will earn its money only when the project is done and after your validation. Therefore, although paying upfront you are the one deciding when the freelancer will be able to enjoy the fruit of its work.
This technology developed by MangoPay allows you to be reimbursed - partially or totally - if a severe issue comes up.
We run a very transparent reimbursement policy, feel free to have a look!