They don't have to do a single thing other than open a case, so that you have proof that you are willing to stake legal repercussions (fines, jail, possible eve

They don't have to do a single thing other than open a case, so that you have proof that you are willing to stake legal repercussions (fines, jail, possible even prison) on the validity of your claim. The sellers don't care whether the police is going to investigate, they only care that you have the legal paperwork that they can give to their insurer so that THEY can get that money back, too. Because you don't get paid "by the seller", you get paid with dollars that the seller gets from their insurer. Until they have the evidence that the insurer will accept, you're not getting paid.