Do you think anybody would pay for wallet recovery service before the fund in the wallet can be recovered? I don't think so and it's only someone that is not sincere will want to get paid upfront before a wallet can be recovered.
I have seen cases of people that looks like scammers asking for upfront before they could work on wallet recovery cases. I believe if fund is inside the wallet, after recovering the fund in the wallet, the percentage agreed rate can be withdrawn after the job is done.
I do not think any right-thinking individual would make such a mistake as to pay for services when their wallet in question has sufficient funds that would be accessed after the job is done, based on the agreed-upon percentage. However, I saw where the team said they would take a percentage based on what is in the wallet when they successfully recover the wallet keys, and I think that is okay to start with, as they do not demand an upfront payment before they commence their job on the wallet.