You said something that got my attention which is in as much we are considering the potential clients in terms of safety, we should also consider the tech firm that did the recovery, I think you are, some client can be funny they may decide to act funny when they know that the service they needed has been rendered although I believe there should be an agreement binding this and again I think once this service has been rendered there should be a terms that has to compel the client involved to reciprocate the same as the service porvider by giving them the agreed percentage.
There should be a mutual agreement between the two parties and the terms and conditions of the recovery firm need to be understood also to prevent future arguments due to disagreement especially when it comes to payment for the service rendered. Some firms that are into wallet recovery do collect from 10% to 40% depending on funds that could be available on the wallet.