I don't agree that the subcontractor should replace lost work. It's totally possible for work to be lost without any blame attached to the subbie.
It's nothing to do with "blame".
Look, you can set any conditions you like into your contract. You can insist they work with one trouser leg rolled up above the knee and wear a red bowler hat if you want to. If they want to accept it and sign the contract then that's the way it is.
So, create a contract whereby they rent the work and one of the conditions is that they replace any lost work. They don't have to take it but someone will for the quick start it would give to their business. Plus, let's face it, if you're out and about cleaning windows, you gain more customers than you lose just by being visible in the street. So, their round will probably increase anyway; keeping the rental payment constant is no real hardship.
Then you're looking at a huge payback despite buying the work at 10x monthly value.
Buy it at 3x monthly (which is the value some berks put on their rounds) and you're in the realms of 80% ROI annually. Madness.
Vin
Vin