Well I really get your point, however this idea of asking for upfront payment is something that I believe is not right especially since the service is in crypto space. So this idea is not okay because so many has used this pattern to scam people. The issue of trust has to come from both sides, if the service provider doesn't trust the people that want to petronise there service I don't think anyone will want to trust them also mutual trust is really important here. It will be a bad I idea to ask someone to for service they are not even sure the company will be able to deliver. Even if they are asking for 30% upfront payment, what do you think will be the fate of those that will petronise them if they disappear?. They should be able to show evidence or a result that they can be able to render this service ,they can start the work then show result of partial recovery. In this way there will be a great trust from there customer.
Everything still falls down to being scam. From your explanation you only understood one part of what I said earlier on. For sure, asking for payment in advance may seem to be a scam from the service renders but subsequently the client may fail to send the payment after they have recovered his/her wallet. In as much as we are focusing on the security of the client let us also look at the safety of the people who give their time to recover the wallets. It's not an easy job and it can be very stressful especially when they are giving less details to work with.