An itemised invoice is one that breaks down each item of the job: the materials with their brand and model, the labour, the travel if it is charged and the taxes, instead of showing a single amount with the word «service».
It lets you know exactly what you have paid for, make a claim if something fails and send it to your insurer after a burglary or other incident. If you have a rental property or manage a community of owners, you will also need it for your accounts.
Always ask for an invoice and keep it with your house papers. With us the quote is fixed before we start and you can pay by card, Bizum or cash. More under emergencies.