The invoice (facture) will itemise each piece of work and cost to protect both artisan and customer, and there are often different VAT rates applicable to repairs/renovations (customer signs declaration that the item has previously been installed, and (last time I checked in 2020), the VAT dropped from 20% to 10% (4-5 years earlier it was only 5%!)
Finally, by having an itemised bill, the artisan can prove that only ab and c were replaced, so a customer claiming that item d had failed after replacement will get very short shrift ... If Item d needs replaced, a new devis will be required
If the business goes bust, any guarantee still in force becomes the responsibility of the French Government. Processes can be long winded, but both artisan and customer are protected throughout
Steve