The purpose of the initial deposit of service workers is "suppose" to be insurance. 2nd its a service owners fault if they leave more than what that deposit was on the account. It gives worker temptation to take. You as a service owner should never leave more than your willing to refund no matter how much you trust your worker. If worker made 10m deposit over a month ago and has done a fair amount of jobs, but then logs onto an account to see that there is 100m on the account. That is 10x his initial deposit and probably more than he made in that whole month.
Tbh its service owners responsibility to keep its customers safe. If they don't take full responsibility or run it like a proper business should be run, then they probably shouldn't be a service owner.
Having insurance would only cause more scams I believe as owners would hire less trusted users to do services as they now have a safety net, in future causing more scams and costing you a ton of money,.
In end its good concept in theory, although completely avoidable. It would never work