SIRET numbers and building
All enterprises registered in France will obtain a SIRET number at the time of registration. This is a number that you can check to be sure that an enterprise is correctly registered and authorised to work on your property.
An enterprise must be not just registered, but registered to do the kind of work that you are asking them to do. The SIRET number must appear on the devis as well as the final invoices - so you can check before accepting a devis whether the company is authorised.
Officially it should also appear on any publicity from the enterprise, but I think this happens rather less often.