Fictional reckoning?

Hello I have heard that there is no fictitious settlement after a liability damage is possible. The opposing insurance wants in any case an invoice and after the invoice is also paid. (The lawyer also prefers repair invoice) And another question, may the opposing insurance simply reduce the wage costs because the allegedly overpriced. Opinion would be made at the ADAC. Total total 1500€uro insurance wants to pay about 250€. less. Ic h wanted the car to repair itself, that I can save something. But if I can no longer fictitiously calculate it is not worth it. Then I prefer to bring my car to the Mercedes and have everything repaired properly with all the new parts. Andreas.